Do you have any idea why I feel cheerful in the early morning and like shit for the rest of the day ?

Serotonin. Maybe you start the day with a high Serotonin level that quickly depleats.

Because early in the morning you probably don't have to deal with humans. Or at least that's how it is for me.

I was like that yesterday. I think the excitement and sense of purpose wore off with my energy level.

Reality sets in?

Drugs
?