I'm coming here for advice.

My friend, who we'll call 'C' for privacy's sake, has been tubby her whole life and recently started putting off weight pretty fast. At first I was concerned that C may have developed an eating disorder, not only because of how quickly she's losing weight but also because she'd been insecure about her size for her whole life, and had just gotten her first boyfriend around the time she had started losing weight. I dismissed these concerns, though, because I didn't notice anything wrong with her. She always finished her plate, had three meals a day, and overall didn't seem to have an unhealthy relationship with food. Her boyfriend was proud of her and was careful to make sure she wouldn't push herself even harder for him. I never heard her throwing up or gagging when we went to bed on the days I sleep over, even though her bedroom is near her bathroom and I'm a light sleeper. That ruled out both bulimia and anorexia.

But last week, when I visited her, I woke up in the middle of the night after a nightmare. It wasn't exactly a nightmare; nothing happened, it was just red. A blank red 'screen', and then I woke up with the feeling of having to pee. So I go out in the hallway and see that the bathroom light is on.

You might think this next part is weird. But we've been close our whole lives, even taking baths together when we were kids. And yes, she is the only one who uses that bathroom.

I go into the bathroom silently. I wanted to scare her, laugh about it, ask to pee, then go back to bed.

She was kneeling over the toilet. I thought she was just going to throw up, maybe she had bulimia after all. But I could hear her chewing. Her breathing was ragged and gravelly like she was just getting over a bad cold. I took one step closer.

She was chewing her arm. I almost laughed, thinking, How itchy could it be?

And then I saw red. Dripping onto the toilet seat, dripping into the toilet, and making those little feather-like dripping noises that water makes.

I couldn't move. I stopped breathing when I saw it. I was sad for her and how bad her mental state was in order for her to even think of doing things like that. I was mainly terrified that she would be chewing me next. But those were all just basic instincts. My first real thought was that what I was seeing was DEFINITELY self-harm, and suicidal idealization, the same things I went to the hospital for.

My second was that I absolutely could not interfere. I know her, and I know how things like this go. I know that when I got caught doing something similar, albeit more 'normal', I lashed out at everyone who tried to get me help. So I would tip her parents off in the morning, tell them to look at her wrists while she's still sleeping.

Then, she paused, moved her arm as if she was raising her hand, blood pouring down her arm and soaking into her light blue sleeve, and spat out her flesh in the toilet. It landed with a sickening plop.

I was disgusted. The red clumps of flesh and the thick smell of blood permeated the room and made it humid. I was sad, seeing the tattered, chewed-up flesh on her arm. I was alarmed, disgusted, seeing the bone, and the yellow fat scattered about.

I'm not the best author. I know I should show, and not tell. But how else do I put this? My best friend is an auto-cannibal. I witnessed my friend auto-cannibalize herself. I'm sorry that I don't feel like making this all flowery for you, though I know this automatically makes it less interesting.

I should've left before this. But I stayed long enough to see her pluck the yellow globs out of her flesh and carefully wrap them in a large velvet pouch with a weird sigil on it that I'd never seen before.

Again, disgust, sadness, the feeling of being rooted in place. But an animal part of me, or whatever other being that has existed in the same material I'm made of now, knows that she is almost done and is about to turn around. I'm smart enough to listen to it. I ducked out, careful, silent, all my pee suddenly evaporating into thin air, the pressure in my bladder turning into a cold, heavy, dreadful mass lining my gut.

Quickly, on silent feet, I get into my sleeping bag and roll over to my usual position which thankfully doesn't face her bed or the door. I even out my breathing. I stab my fingers into my palm to make sure they don't go through and that I actually am awake right now.

I hear the toilet flush. The sink runs. Footsteps, a door opening, footstep, door closing, footsteps, and on and on until she finds her way back into bed. I don't notice any unusual sounds, no crying or sniffling or anything that usually accompanies self-harm. She goes from the bathroom straight to her bedroom.

I wait until I hear her snoring softly to release some of the tension in my body. It took about 10 minutes of staring into the blackness and chewing on my lips, but I finally work up the courage to check her out. For her safety. I remember specifically the thing that got me out of bed was: "Remember this is still your C."

So I get up and tiptoe over to her bedside. Cautiously, muscles burning and my heart about to implode, I fold her blanket in half and check her wrist.

It was gone. Her skin was... well, I'll skip all the flowery language. Her skin was actually there. There was no trace of her teeth or of blood or anything. I checked her other arm. No bandages, no blood, nothing. I would've smelled her breath, but getting that close to her might have actually sent me into anxiety-induced cardiac arrest.

So I tuck her back in, tiptoe back to my sleeping bag. At this point I'm seriously concerned that this was an episode of hysteria or psychosis, but nothing particularly out of the ordinary has been happening with my lately. No other symptoms, though, and there are usually signs before someone experiences psychosis that vivid. I mentioned I've had a history of mental illness before, but nothing related to shizophrenia.

But now there is no doubt in my mind that everything I smelled, heard, and saw in that bathroom was fake or imagined. My imagination when I control it isn't even that vivid. Even my dreams are blurry, like I've taken my glasses off. That was real.

So you can imagine my confusion when not only was her flesh intact, but there was no sign of it ever happening in the bathroom, even though I woke up before her. It's reasonable enough to deduce that she cleaned it up herself, but that fast? She left the bathroom moments before I did. I scoured the bathroom but couldn't find the pouch.

Her mother was downstairs making breakfast. I don't think I need to clarify this, but I didn't have any sort of appetite. I went back into the bedroom to get dressed. She was sitting up, awake earlier than ever, no blood on her, no teeth marks. She was wearing the same pajames as last night, not a speck of blood on them, just the gravy stain she'd gotten last night during dinner. She could not have gotten up to clean it. I was awake the whole night.

She was oddly happy to see me, even though she was the exact opposite of a morning person. She was usually grumpy when she woke up and insisted on the 5-more-minutes rule, but this morning, she practically dragged me downstairs for breakfast (which she never threw up, and I was there until noon when my parents started pitching a fit over my absence). I couldn't stop looking at her. She was glowing, healthy, smiling, joking with her mother, planning what to do for today. At one point I was staring so hard she had to ask me what was wrong and, jokingly, if there was something on her face. Her mother was worried about why I wasn't touching my food after they had all finished. I couldn't tell her. How could I? Who would believe me? I told her I didn't feel well or something lame like that, I don't know.

Fast forward to today. She looked amazing. No loose skin and she was even developing an hourglass figure and a thigh gap. Her clothes were looser. She was healthy and whole. She was happy. And I love seeing her happy, I love that she's proud of how far she's come and how well her life is going, but whenever I see her, all I can think of is her bent over that toilet and eating her arm.

It's ruining everything. I cannot enjoy myself around her. I find myself constantly worried about her mental and physical health, and worrying about how to proceed in a careful way so that I don't lose my closest friend.

I don't know what to do. Is this a psychological issue, even though she's happier than she's ever been? How do I help? Do I have a right to interfere? How do I get proof? Who will believe me? What is she even doing?

Please let me know what to do. I can't lose her.

EDIT: This will be a series. Thank you for your help.