When it went on its side I started to panic. It’s now in a dark container with a heater and airstone and water from my reef tank which I know isn’t toxic. I’m going to leave it overnight to try and keep it as unstressed as possible.It's way too early to tell, or panic. He doesn't seem overly stressed from what I can see, The yawning thing is to clean his gills, just notice if a he starts to shake his head. The yawning with a head shake could be an indictor of flukes, which eels do come in with often. Did you happen to test the sg in his transport bag, some suppliers run low sg to suppress disease and parasites, and a high rise in sg can cause as issue. You kind of have to give it a little more time, just make sure the water quality is right. Moving him will just make any stressful situation worse. Is that rock structure set up in a way he can burrow into, if not move the rocks around to give him the opportunity for some cover. I would definitely offer him the live ghost shrimp, that will be a true tell if there's an issue.