Indie is home. He has been seen by his his regular vet. She agrees with the ER that it probably was due to fleas. Even though they're treated monthly they still get fleas. I have to change flea meds every couple months to try to stay on top of it. He goes back tomorrow morning to have his blood checked again. She wants to make sure that the red blood cell count is stable or rising. She also put him on an antibiotic to handle any infection because of flea bites.
He's settled in and I put him in my office. That is the room that the cats normally do not go into since I keep the door closed. Last night I sprayed it for fleas just to make sure there were none in there. So far he seems to be acting normal including eating and drinking.
Thank you so much for your prayers. He still has a ways to go to be back to normal, but so far, everything seems promising.