I get those all the time. Since I started lucid dreaming I've generally been subjected to all kinds of strangeness at night. I've mentioned my vivid and usually terrifying hypnopompic hallucinations, usually living things (a pale hunched troglodyte, a sackcloth dummy with grass for hair, etc.) that watch me from around corners and slip away as soon as I realize they're there. Another common one is disturbing images that imprint themselves on my vision even when my eyes are closed, the one I remember most clearly is a clown face in inverted retina-burn colors. I also, especially after a lucid dream, tend to have long chains of inception wake-ups, sometimes doing it three or four times. A long time ago I was lucid dreaming almost every night and every time I had a lucid dream I'd false-wake into a nightmare version of my house. Those nightmares were always identical in layout and general events, I was lucid but I was always too freaked out to control them and each time they lasted a couple minutes longer, I was genuinely beginning to suspect that the nightmare was the actual real world and this was the dream and eventually I'd wake into it forever. Basically lucid dreaming has eroded my sense of reality so I'm no longer certain that any of these layered realities I travel through is actually "real" in any permanent and stable sense, including the one I'm in now.
I used to think solipsism was silly because there's no difference between a "real" universe and an illusion of one, but lucid dreaming taught me the difference because now I've been in control of the fundamental structures of a contingent reality. If this universe isn't self-sufficiently real then it, like a lucid dream, is contingent on an outside reality and changes to the state of that meta-reality could lead to drastic changes in this one and it's literally impossible to predict these changes because they're sourced outside our reality. You could wake up tomorrow and everyone is you and every you believes, like you yourself, that he's the original you and you're one of the inexplicable clones. Or the universe just ceases to exist or rearranges itself on such a fundamental level that nothing that currently exists is preserved.
Things that terrified you today.