Hearing/seeing things that aren't probably there?

I do not regularly smoke marijuana, the last time I smoked was a few nights ago however every now and then I'll hear something and have to question if I really heard it. Or I will look at someone, and they look fine and then they almost look scary (their eyes look really scary) what should I do? Is this normal?
I've never ever experienced this before.
Hearing/seeing things that aren't probably there?
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