Five days ago i was mulching and when i stood up i hit the back of my head hard on a cement overhang. the worst symptoms i had were pain, fatigue, and perhaps mild nausea. today i noticed one nostril slightly dripping. could this be brain fluid?

Unlikely: CSF leak isn't that common, and the trauma you sustained is relatively of low impact, however if you are still suffering other symptoms , you may want to see your doctor for assessment and reassurance, best wishes

Head bump: Your head bump needs to be evaluated by a doctor. You may have had a concussion. The brain is enclosed in the skull so the fluid from your nostril is more likely from sinus. Please see your doctor. Peace and good health.

CLOSED HEAD: injuries can be "tricky" and cerebrospinal fluid leakage can be spontaneous and also may occur after relatively minor head injuries. That being said, it is very unlikely that this is true in your case. The headache from such CSF leaks is usually SEVERE!! I suggest , however , that you have an in person examination with a Health Care Professional (your own PCP or an Urgent Care Center. Z