Question about cognition and science of chess players

Hi, this is a serious question and I hope I could get a serious answer. Especially if you know some psychology or psychiatry. What factors affect chess players who may have been playing well and after a month or weeks pass they simply cannot win as many games or make blunders. I don't mean to ask whether it happens. I know it does happen to most players, from what I read.

But what factors actually may be affecting this? Is it distraction with certain types of non-chess related information? If so, what do you think affects the analytical ability, concentration, or patience of a player? Maybe experiencing adrenaline inducing events? Maybe not enough adrenaline? Serotonin or dopamine levels that could affect the mood? Something like caffeine?

Maybe some type of music? Lack of sensory stimulation or too much stimulation? Blood flow and oxygen levels in the brain?

I appreciate any more or less scientific answers or insight. Thanks!

Dayum, I get no responses....

I can only speak from experience. First of all, even if you feel totally fine, normal, good energy, focused, etc, that can be a lie  If the body were miserable every time it wasn't at its peak, then life would be terrible hah.

So in my experience it's one of these:

8 hours of sleep each night for the last few nights?
Eating regularly and at least somewhat healthy?
Anxiety or stresses (job, family, relationships, money, etc)
Dedication to performance (are you consciously committed to playing well for this session?)
Other physical (done any exercise that day?)

Usually you can violate ALL of these and feel more or less fine... even if it's a little extreme like staying up 24 hours or not eating much. But it will hurt your performance.

Here are a couple technical things I know about learning that may help:

(1) Local optima. Both humans and machines typically reach a point where it seems they have optimized their performance, but in fact they haven't: they have reached only a local optimum level, like the top of a hill in a larger landscape where there exist mountains. I'm not certain how this problem is overcome in general, although in machines I believe data outside of the usual range helps, especially with more prevalence, and in humans I believe new insights or knowledge is the key. Applied to chess, that would mean learning new concepts, especially from books or from higher-rated players.

(2) Change of algorithm. This is similar to (1). Sometimes the problemsolving method being used is flawed when used on more difficult problems. I particularly ran into this problem in Tactics Trainer when, after seeing my score steadily increase, it started to take a very noticable downturn that never recovered. What I didn't know then, and what this site didn't mention, is that Tactics Trainer problems get progressively harder as your score rises. What evidently happened is that I learned one algorithm to give me good TT scores on easier problems that no longer worked on harder problems. That's why I dislike TT and soon gave up on it permanently: all I was learning was how to boost my TT score instead of how to play better. I didn't feel like having to keep learning new, ad hoc, beat-the-system algorithms that would need to be replaced at some point, repeatedly.

P.S.--It wasn't clear to me from your description if you were playing against progressively more skilled players. I assumed you were, but maybe you meant your performance is decreasing against players whose strength hasn't changed. If that's the case, my comments above won't help, and I can give advice only from my own experience: I've had that problem arise from increasing carelessness with increased confidence, especially from getting lazy about looking at tactical possibilities because I know my positional reasoning is sound. In chess you can't ever safely dwell in an ivory tower of positional knowledge while hoping that such general knowledge will overcome weakness in tactics. Tactical considerations will seep into any such ivory tower!