I'm pretty sure that an after-effect of pot is depression. Go to erowid.org. It lists all the various effects of it, ranging from desirable, neutral, to undesirable. I think I read that depression was an undesirable effect, specifically after the high...obviously.

I know the first few times I got high (actually in the last couple months), I felt super awesome the next day. Now, I don't feel super awesome, but slightly irritated and tired. But that could just be the drag of work and school. Dunno.