Are we looking at G-LOC here guys and gals?
That did spring to mind.
I had my own G-LOC experience in the 1970s while flying a Harrier GR3 back to base from a field deployment. After take-off from the site I had accelerated away, hard-turned starboard and reversed port all at about 4g. Pulling up into a wingover to come back for a site beat-up I blacked-out and came to as the nose was slicing down through the horizon at about 120 deg of bank. I rolled wings level and flew back to base at a sedate 2000ft and 400kts even opting for a practice PAR instead of a run-in and break. Nearly became a statistic that day at age 27. G-LOC is insidious and can occur at surprisingly low G. Fatigue plays its part I'm sure as does low blood sugar. It wasn't a great idea to go without breakfast as one of my contemporaries found out.
The other possibility is controls being snagged on flying kit. The Gnat is tiny. One didn't so much get into it as put it on. In the 70s RAF pilots wore internal G-suits underneath flying suits. External G-suits didn't come into use until later. I wonder if the control column snagged on something.