[ak39]

Are you getting quality sleep at least 7 hours a day? If not, fix this. If you are, don't think you need to be worried either.

Uninspiring work can cause sustained and unhealthy stress in the best of us. And stress is known to deplete cognitive abilities. It's probably stress.

[davymac]

+1 on the quality sleep. if you wake up with dry mouth or drool regularly, you're mouth breathing during sleep which is commonly a warning sign of sleep apnea, which causes loads of problems, especially mental health probs.