I have a similar (albeit modified) theory. Let me clarify that stupid and smart don't necessary mean the same as regular usage, but they're close enough.
If you are 'stupid' (not necessarily intellectually, but in some ways), the neurosis (psychosis is a strong word, no?) is less, you don't think about things you shouldn't (bothersome, existentially) and you have a healthy and comfortable intellectual-emotional life.
If you are very smart/smart, you can get beyond the temporary plateau of 'thoughtfulness' that also brings neurosis. You think about things that are bothersome, but you have enough mental strength to overcome and suppress them. You're high-functioning intellectually, and it doesn't take a toll on your psychosis.
If you're in the 'middle', you tend to think about things, and keep thinking till you've found reasonable solution. It is bothersome, depressing, and often not pleasant. But you have the gift of 'thinking', and you like using it. It's a stimulating albeit mentally tiring existence.
When you say you're 'dumber', I interpret it as you saying you've trained yourself not to ponder upon things that will lead to no obvious outlet. Maybe you've genuinely trained yourself to never think about certain things, maybe you've trained to control your bothersome thoughts on command. Either way, you've trained your thoughts to a 'different level'.
/armchairAnalysis