Try writing stuff down (on paper). It doesn't have to be detailed; bullet points, rough sketches, or even illegible scribbles can do the trick. Write/draw whatever you want, and whatever pops into mind.

The point is, if it's written down somewhere, it kinda removes pressure to try and remember everything, and you can then move on without worrying about it. If/when you come back later, the notes will remind you of the thought process you had going on at the time you wrote them (although over enough time, anything cryptic might get a little harder to recognise). Some of it might end up being useful, some of it might not, but that can be decided at a later time. For now, just dump everything onto a piece of paper.

I have a bunch of tiny little notepads (at home, at work, and in my bag; I have at least one wherever) for just this purpose. Pen+paper seems to work better than typing for me, but that could also work.

This is just my experience, so it might not work for you, but it is something that helps me. Good luck :)