Seems fair if you can guarantee that the bunk bed won't break. I've seen bunk beds that break pretty easily. If you can get something stronger or a higher surface, that could work.
Otherwise, seems like a fair setup. Just check if it can even handle that weight. You need approx 3 kg to counteract the pressure in your carotid, so do the math (F/A, where F is Force, and A is Area for the belt.) Just put in your weight into a Newton calculator, then measure the belt, and if it exceeds 15 kPa (the pressure of the carotid) then you are good.
Remember that this is a permanent decision. If you fail, you may end up brain dead 10 minutes after your attempt due to brain cell death. You literally can't recover even if you are saved.