I know this partial blackout/stage-fright feeling all to well. Found two things that helped me:
- Have a small paper at hand listing a small number of keywords for possible patches/parameter changes. In case of a blackout, reading any of the keywords gets me back on track.
- Remind yourself you have the freedom to do anything. This can become a keyword on said paper as well.
I use (1) since last year, and learned about (2) last weekend, where I played at a small venue with 5 other acts, and as the evening progressed, the timetable became more and more messed up, so I ended up having to play in front of the stage while one band was tearing down their setup on stage, followed by the next band settting up their stuff – and neither of them were doing it exactly quietly. At first I felt rather uncomfortable, but all of a sudden I realized “this is disturbing already, so I can’t make it any worse, so I am free to play whatever I want” – and played one of my shorter but more emotional sets so far.