Lovely OT made it very clear she was expecting me to be an active user of my chair. And take risks. And she also made it very clear that I would tip it over at some point. It's about finding your balance, so it's like riding a bike. You'll fall off a few times. You can add anti-tip wheels to the back of chairs, kind of like training wheels, but they add weight and can prevent you getting up a kerb. So she doesn't fit them.
The inevitable happened on Tuesday night. A good combination of a slightly too steep ramp, rookie mistakes and not paying enough attention. It happened very quickly but I did manage to do what I had been taught, which was to bend my head forward, so I didn't hit it. Surprisingly I didn't really injure myself at all. The back of the chair doesn't have a cross bar that is flush with the back, but one which curves out so there is about 5cm clearance between the back of the chair and bar, so you end up lying on a padded hammock. The only bruises were to my ego.
For now, though, I am being a bit more careful with slightly too steep ramps!