If I fell of a stool while at a nightclub when it broke to pieces and I am in a lot of back pain, is there anything I can do if this happened 8 months ago?

If the nightclub was at fault in some way, then it is possible that you could sue them and try to recover medical costs, lost wages, and some amount for pain and suffering, if the pain (or resulting disability) is serious enough. The issue is fault--if the stool was damaged, broken, etc. previously, and the nightclub knew it presented a hazard but did not take care of it, that failure to take care could result in liability; if there was no reason to know that the stool was a problem, it may be difficult to establish their liability. And, as noted, unless they voluntarily offer you something, you'd need to sue them for the money, which has its own costs in time and money.