That sounds like it could be an olfactory (nose/smell) flashback. There are also auditory (hearing) and visual (seeing) flashbacks.

I experience all three types here, yonder and there.

Mine are directly linked to my C-PTSD, but yours may not necessarily be trauma related like mine are.

If you have a therapist, y'all can explore their source in therapy, and if not, then there are plenty of resources available online about them.

I used to think I was crazy and had gone totally off my nut when I'd have them.

Now that I know their source, it doesn't freak me out quite so badly and sometimes I even enjoying trying to puzzle them out.

I wish you the best in exploring yours.