Clubby, watching that video positively sent shivers down my spine. For different reasons (broken legs), I was in the same situation 35 years ago. I spent a lot of time on an exercise bike, gradually lowering the seat from impossibly high, to ridiculously low, as the range of motion improved. It was a long, slow process. The most interesting aspect was the discovery, once back on my bike, that, standing on the pedals, my right leg would just stop when the pedal was at about 10 O'clock (Freewheel bike). There wasn't any pain, it just would stop. Finally I got PO'd, and figured a spin on a fixed gear would be the cure all. It was. Still have restricted limits of motion in both legs, but more than enough for most activity (no limbo for certain!).

Carry on, you'll be fine.