sounds like pseudo-hallucinations rather than delusions.

(you have insight fairly quickly into the fact that they aren't real)

do they tend to happen when you are feeling very anxious / wired??? that is relatively common... i would say that emotional stress induction would be a more likely explanation than head injury.

do you have olfactory hallucinations (funny smells)?
how about seizures?

(thinking a little about TLE - temporal lobe epilepsy)