Lizards definitely dream , and they do have nightmares too.
I have seen this kind of thing with Lucky and Wriggles ( blind terror hours after the lights are out when they'd been sleeping soundly for ages) , both were rescues.
Both were absolutely terrified of the sound or sight of cats and dogs and large birds, and both were also very scared when the hairdrier or vacuum cleaner were on, or when the mower guy was here to do my lawns and edges (I'd have to get them out of their tubs and place them inside my shirt on my bare chest or tummy or on my shirt pocket to settle them down, I was told by the vet they considered me their safe-place.
Same with my BTS.
And I've seen it with all my beardies. More often it's legs or arms or tail twitching in their sleep or even what looks like little chewing motions .... guess what they are dreaming about ...
The same will be happening with your beardie.