Ive stopped both Copaxone and Avonex in the past. Once because I needed a break and once because I was pregnant. Both times I did very well for a few months, and then BAM
....so I went back on.
I have missed my shot for 2 days at the most (recently) and have not had any significant issues, however the longer you go, I would think the more chance of something happening...as for the hyper feeling...I dont think I have ever experienced that....