Need an answer from a Math viewpoint ( and thank you guys in advance)

Recently I have noticed a definite trend in my cash games : Inability to maintain a big (or big-ish ) stack. I can run up my stack very fast, but whenever I get
a large stack, I lose it equally fast. And it seems like I always lose it. If I buy in for 100/200 in a 1-2 game and run it upto $700, it always goes back down; ts never in the other direction (as it used to be in the past, when I would regularly book over $1000 cashouts in 1-2 games). Now the reason for most of these things is lack of skills, and I am sure thats the case here too. But I am a winning player overall, (always been, even though these days only barely), so there has to be more reasons than my
general 'donkeyness'. Mathematical ? Psychological ? I am a lose and active player, maybe I am
being too active with my stack ? But its not that I am being too cocky and raising with 2 3 offsuit; I still try to play logically and hold on to my stack. But I cant !
Even online, I was playing 1-3 heads up and ran up my $60 to $450 pretty fast ( and by playing good, in my humble opinion). And then sure enough, I lose it all. Any thoughts , advices ?

I would post this question in the forum best suited for the stakes and games you play.

what do you mean ? any suggestion ?

I mean this is a theory forum and your question isn't really theory related. It would be better to pose your question in either the beginner's questions thread or in the forum for the game type (holdem, omaha, stud, etc) and stakes (high-mid or low) you play.

People there will have more practical experience that can better provide answers to your questions. You can even ask a moderator to move this thread instead of starting over.

If I had to guess you are just a victim of variance. Either an initial run of positive variance that is catching up with reality or a current run of negative variance that may or may not end before you can't afford to play anymore.

Most likely, you are just overly concerned with the lolsmall sample of actual hands in this trend. You would need maybe 6 months of live poker to be sure something is wrong. Most likely, you just need to study some on deep stack poker, and make sure you are not blundering your stack.

IF there is a mental problem it is likely this:

Behavioral Economics is the study of how humans make incorrect decisions about money, risk, AND POKER, because of several different laboratory tested proven human responses.

One of the key concepts is fear of losing something that you have earned.

If you earn a big stack by playing well and taking the appropriate risks, then most humans will start to play less risky and avoid the correct risks in order to try to preserve that big stack. This leads to bad poker decisions.

OR...

Another key concept is ‘mental accounting’ which is when humans mislabel their money according to where it came from. These people will view a large stack as “House money” (or other poker players money). So, they get too loose and risky with the big stack. This leads to bad poker decisions.

Those are just two examples of behavioral economics. There are more, and it is interesting so check it out.

Thanks guys