Brumation or Sick-Please Help

Hey guys!
First time beardie owner here. Aladar has been a part of the family for about 1.5yrs now, we got him when he was just old enough to be determined a male. Yesterday he was so lethargic I took him to the the exotic animal vet clinic we typically see. They found nothing wrong with him after doing bloodwork and x-rays, everything checked out to be perfectly normal and healthy so we assume he is in brumation for the first time.
He was moving about a bit (although extremely lethargic) yesterday afternoon after his weekly soak, when I came into my office today he was asleep as expected but his beard had turned black and his mouth is slightly open and crooked. His temps have recorded all usual, his lights on the timers are all working normally, humidity ect all normal.
Has anyone else experienced a blackened beard and open mouth during brumation?

Also, I definitely cannot see if he is breathing and he has not moved at all today.

Hi there, sorry to hear about Aladar. The open mouth + black beard indicate extreme stress. Can you pick him up + see if he's still moving ?

He is not moving at all. I picked him up and he seems to be limber (possibly because he is on the warm side of the tank), not stiff but zero response at all and I cannot tell if he is breathing.

Something happened that made him seriously ill and did not show up in the bloodwork. This does happen sometime unfortunately. Turn him on his back too see if he even tries to turn back over, do so for just 30 seconds and then on his side. You should see a difference in breathing due to positioning him differently. If you can not get any response at all you might decide to take him back to the vet [ some people would suggest ] but it may be too late.