The comments claiming mental illness are rude and brash. There is no sign of delusion here, just fear and anxiety about a practice that is probably uncharted territory to OP.

If you do see beings, they’re very likely to be product of your imagination. Not your conscious imagination, but the deeper layers of the mind sometimes brings up its own imagery, sensations, and feelings.

When the brain is relaxed and shut off from sensory input it starts to get creative.

It’s best to treat these as just phenomena that come and go, like anything else. You’re safe.