Reason For Slide In Cognitive Ability? Have High Stress

Hi, I am concerned about a strange slide in cognitive ability which has developed over the last few months. My ability to do calculations, follow through complex logical patterns, visualize virtually anything, and in general deal with non-literary issues has dropped very significantly. I am a programmer, and I find this very disturbing. There are no known environmental factors I can think of, my stress is high but it has decreased slightly the last few months, and I have in fact been getting more sleep, so I don t understand why I have suffered a disturbing drop in these abilities. I fear I may have suffered some sort of brain damage , because this is more than an inability to focus. Thanks.