I think there are other problems with stasis - we aren't really built to do that. The cognitive process during that time would need to be thoroughly investigated - are you just in some long dream? Do you cycle in and out of dreams? Each person might react different and extending the period may introduce additional physiological and psychological concerns.

Based on what we typically see with comas, I'd estimate we could do something like 5 years kind of safely - but beyond that, probably pushing insanity or coming back as what is essentially an invalid.