1. Watching bad American tv at 4:30AM feeling like it's 6:00PM - which, of course, it is.
2. Waking up at 9:30 AM and feeling like it's the middle of the night, even though it's actually either 9:30AM or 5:30PM.
3. Skipping out of a session at 2:00PM because you can no longer keep your eyes open.
Hopefully I'll get over it by tonight otherwise it's going to be an interesting week.
EDIT:
4. Realising at 4:30AM that 9:30AM is actually 1:30AM, so not an unreasonable time to feel like it's the middle of the night!