Fell off my high bed - does numbness on the inside of my forearm mean that I have nerve damage?

No. Your nerve was injured, for sure, but probably not damaged. Like a muscle that gets sore after it is bruised or injured, a nerve can do the same thing. Its reaction to the injury can be either pain, like when you hit your funny bone, or numbness, when it is shock, so to speak. Either way, unless the nerve was actually severed, it is very likely to be fine within a few days.
Yes. It depends on the severity of the contusion or injury to the forearm. But yes numbness could be a sign of nerve damage or if less severe- just a temporary nerve injury. Often times these injuries are less severe and as a result the numbness simply goes away on its own.