Years ago I looked into lucid dreaming and found that those communities have catalogged several actions that can act as “reality checks”.

Generally in a dream, some things pretty consistently don’t work right. Time/watches, mirrors, light switches. Check one of those and see if anything looks weird. If it makes no sense, probable that you’re dreaming.

Try to remember the sequence of events that led to what you’re doing now. In a dream, there wasn’t anything before.

Or my personal favorite, plug your nose and then try to breathe through it. In a dream it will work.

There’s quite a range of other methods out there too.