I’m not totally convinced that SP hallucinations and/or ghosts are ALL due to one’s imagination. I think when in between sleep and waking, the usual barrier that keeps most people from consciously being aware of spirits and the like is lowered so one may be more likely to see real ghosties when trying to sleep (or being awakened during sleep).
Maybe some of these hauntings could be attributed to HH , but I don’t know if anyone can really determine the percentage.