I feel the same way. After a certain point in the day, things suddenly just start flowing and usually it's not that I feel over the top high just pleasantly normal and healthy. Having not been able to work full time for a while, a lot of times if I go to sleep at 6 or 7 (am) and wake up at 3-4 PM, the whole day just flows perfectly more or less. When that's disrupted, all kinds of things go wrong. I can remember having awful feelings of dread in the morning and early afternoon in college and grad school. And something just feeling right after late afternoon / evening.

Bipolar is closely related to sleep sensitivity and circadian rhythms so it may be something worth looking into. I also have obsessive tendencies, score at the close to Asperger's level but not quite on most simplistic tests and possibly would have ADD if were tested as well. Additionally, migraines whose most extreme appearances have mostly been under control. Best to you!