Part of my research into the rationality domain comes from the Center for Applied Rationality. They have a great website called Less Wrong, which is dedicated to discussing research on how to make better decisions, think more rationally, and that sort of thing. They have an incredibly knowledgeable slate of experts who are both academically expert and practically experienced. So I learn a lot.
They had an article in May (yeah, I am a little behind) on Doublethink. The article is a really effective point-counterpoint format that talks about epsistemic rationality (being rational in terms of believing what is really true and acting accordingly) v instrumental rationality (being rational in terms of doing what is in your best interests and believing accordingly). I can see advantages on both sides, so I thought it was great that they presented arguments on both sides.
I often mention that I am a fan of instrumental rationality (self-delusion when it serves the purpose of increased happiness), but of course I am often being a little tongue in cheek about it. The conclusion of the article is that there is a dark side of instrumental rationality. They suggest that somewhere (perhaps unconsciously, but still somewhere) you know that it is false. And the effort it takes to suppress that thought creates a dissonance that can build up and may slide in to your thoughts later, causing confusion or just higher mental workload and stress.
They don't talk about whether this accumulates into any serious long term consequence such as a mental disorder of some kind, but I suspect that it can. It is OK for short term diversions, but not as a long term strategy for happiness. Oh well. It was fun while it lasted.