This is very true, and I guess it's one of the things I didn't realize before I started.
Like many of you, I think I understood in theory what would be expected of me, I just didn't realize how much of myself I'd lose in the process. Especially as a second year, my chronic level of stress is insane (I'm always behind), I'm constantly overwhelmed and it's taken a toll on my relationships. Last year, I was so miserable studying crap I had zero interest in that my whole family was apparently worried about me. This year I just have no time to talk to them. On a basic level, the things I figured I'd like, I did like; and the things I figured I'd hate, I did hate. I just didn't expect how much that hate would eat at me, and how frustrated I'd get. Nowadays, if I go to lecture and the lecturer is bad, I get incredibly angry at having wasted a full hour of my day on something useless. I used to be able to go to lecture and accept what was going on. If a friend surprises me and tells me he's coming to visit, I get annoyed at having to reschedule stuff, while I used to be happy to see people. Any change in my routine, anything that takes up time, anything required that isn't immediately relevant for my next exam- it makes me crazy.