Massive Red Stag tranquilized with Bam- now he can't hold his head up. Help!

We have a small red deer operation, and our best three year old has an issue on his belly that we had to dart him for. We darted him once early in the week and applied some antibiotics. That didn't appear to help so Friday we had our vet come out and we darted him again. Took two doses of BAM but he went down with no issue. Took him a bit to get up after the reversal, and he kept walking around with his head dropped tilted left and right. He is a good 600" of velvet so it must weigh a lot, and we thought it would get better with time. We are about to start day three and he has not improved... on day two he came to his senses enough to find shade because it's quite hot out. He also drank some water but hasn't eaten anything as far as we have seen. Has anyone ever experienced something similar? Is he a goner or is it just going to take several days to wear off? We are a closed CWD Free certified herd, in a state that's only ever had 2 cases that were a few hundred miles away, so it can't be anything related to that.

Update- we used a tourniquet and cut off his velvet. That helped immensely. With how hot it is and him probably having a fever from the belly infection, he just couldn’t keep his head up with all the velvet weight. It isn’t an issue related to BAM as I first thought it might be.