I sometimes get the classic "What am I doing with my life? Where's my future going? What do I have to show for being alive?" type of thoughts when I smoke alone.
The funny thing is, and I'm aware that this is probably just me, but I only seem to get it when I smoke alot of shotties over a short period and lying on my bed watching tv at 2am with big ass glazed over eyes, I dunno, I just tend to look at myself in a different way then usual and I get into a train of thought of criticising myself and thinking of all the bad qualities to me.
When I smoke with friends and/or use stronger smoking methods (blunts etc) my mood tends to shoot through the roof and I get a big confidence boost (I'm a pretty shy person) -- last night I even called my girlfriends sister, pretty much a stereotypical mother-in-law, a shallow carcus and told her to never speak to me again. And usually I always take what she says ("you're not good enough for my sister" etc) with an embarassed look.
So yeah, to round up, try different smoking methods and if that doesn't help, just try to cut down your pot use to a social aspect (of course, if you don't already) and only get high with some good friends and not with yourself. And if it's still that bad then you're just going to have to consider whether or not it's worth it.
But then again, I haven't been diagnosed with any type of problem so I don't know anything for sure, this is just some personal notes.