I was hiking in a wilderness area...a very remote trail without a lot of action, and at one point I heard voices...I swore I heard human voices.
It was up in the mountains, too, so there wasn't much to make noise like that.
Obviously, I know it's my brain hearing trees groaning in the wind and quickly shortcutting to, "must be a human voice!" But it was just eerie.
Foxes and cougars make really frightening sounds, I have often woken up in a cold sweat from hearing their cries. It can absolutely trigger nightmares when you're sleeping, or startle the shit out of you during the day. At times I've been genuinely torn whether I need to investigate someone in distress or avoid a cougar.