I've wondered the same, a medium said that one around me was of negative energy that referring to have been a man once or felt like that. I agree, mine has not been in a very positive mindset, and even if one happen to be so, then you kind of know something is going on (not positive) close by.
The medium kept pushing the envelope, and in return - got suddenly sick, as if it was warning, and had to cut it off.
Lots of times I have not been sure if I really see it right or imagination but have felt a sort of presence, felt something, and someone watching me. But then told myself silly to think that. If I have seen some then they move real fast.