Ok, so still not sure why it’s happening, but I’ve found out how to fix it in case this ever happens to anyone else.
If you go into particle edit, and it does this, all you have to do is toggle children off, and then go back into object mode. Then, when you go back into particle edit, the strands should be relaxed again, and you’re then able to toggle children on again. That should then be fixed until you open Blender again.
I’ve also found that Blender is just closing if I try and edit a particular particle system. A work around is to disable all but the one I want to edit, and another one, and then select the other system before entering particle edit. If I then select the system I want to edit, it works as expected, but if I select it and go straight into particle edit, Blender just closes.
Weird…