As it happens to me, and for what it appears on the graphs shown, downswings usually *begin* at a couple of bad beats. But then... they just go on for a while when "nothing seems to work".
It's simple: after 1, 2 or 3 bad beats many of us are not playing the A game anymore.
I had a horrible session today; only had AA and KK once each, no action on both. Lost with AK every single time. Etc. But was slowly getting a bit of $ back.
Then I isoraised a fish and flopped a straight on duotone board. Managed to get it in OTF, fish had two pair. Turn, he hits his 4 outer to full house.
Of course, the guy is a fish (playing 65/5 or so) and I feel like #(£*&*% to get my $ back from him - and much more. If I was playing my A game it would probably be +EV to stay on the table and indeed take his money. But I know I'm frustrated so that's why I'm reading the forums now 
Study tilt, and study how it works on you. Identify when you are starting to tilt (it's subtler than it might seem) and stop playing every time you reach there. Stop, take a break, walk, read the forums, study, watch a video, post the hand, anything that works for you. But playing while frustrated is a receipt for busto.