I know because in my experience the 2 are very different.

The dead bring messages, while my brain is just out to nonsensically disturb me. Also, I don't personally see the dead when I'm awake, they come to me in dreams, although I do sometimes feel them. And when they are present, its kinda obvious. Eg. My bed will creak and the mattress sink in as if someone sat down.

NB. Sane people have witnessed this happen in my room no worries, its usually family members who refuse to fk off and commit to the afterlife.

In my experience the dead are much more familiar than my brain's newest circus act. I've been privy to other worldly things since childhood, while this particular circus act only started a few years ago when my bipolar peaked.

Uhm, so that's how I know, its just 2 very different experiences. I would never tell a pdoc though, I'm sure they'd have me committed before you could say "ghost"!