How long should you monitor yourself if you bumped your head (without losing consciousness?) for underlying injuries? Can stop worrying when?

Tell us more. Please tell us about the nature of your injury. Most head bumps do not produce any damage because the skull bone is very strong and not easily damaged except in older folks. I would not worry about it unless you developed any new symptoms like persistent headache , dizzy spells or anything that is making you feel unwell. Right now you seem to be fine. So stop worrying/monitoring yourself & relax.