My mate fell off last week just messing about on the morning, only on like a skinny under bar height wall.
fell off backwards, bike hit him in the back of the neck/head.
he like layed there at first then started having like a fit/seizure type thing, shaking, drillbling and his eyes rolled into his head.
was sooo scared :\ he was out riding 2 days later and was fine pretty much just afterwards.
:helmet: