Horse freaks out in stalls.....?

Horse are herd animals and thus need others around them to feel safe. He obviously doesn't feel safe where he is. Best thing to do is work on making him comfortable, if its the trailer he's worried about, get him in and out and get him used to it. If its solid stalls, again, make it a calming atmosphere or just try and find stalls that have ways for him to put his head out. Or you can look into getting him a buddy, race horses will often have a goat or a dog that stays with them to make different situations easier.