It sounds horrendous
you shouldn't be able to bend or twist most of your back - but you should have movement in your hips and in the 1-2 unfused vertebrae you have at the bottom of your fusion. Bending will be done from your hips, and twisting will be very limited. Is it pain that prevents you from getting up again once you have bent over, or can you physically not manage it?
"Having to slouch" doesn't sound good, especially when you are walking. This can sometimes indicate a problem with the way your spine is balanced post-op, and is something you must make sure Mr Evans knows about when you see him (NB it is definitely a Mr Evans you are seeing, not Mr Evan Davies?).
The reason the ambulance men make you go to the toilet is that inability to use the loo can be a sign of serious neurological problems which may indicate an emergency. It's a good sign that you can use the loo and that they leave you alone, really, even if it doesn't feel so at the time!
Were you given any physiotherapy post-op?