If you watch a horse get up, the first move they make with their legs is to shove the front ones out in front of them, to push themselves up. So you definitely don't want to be up there at their head. If you HAVE to get close to one that is laying down, the safest spot to be is on the opposite side from where their legs are, but you have to pay attention that they don't go to rolling (they don't usually, but you still need to watch for it).
If I go in a stall to get a horse who is laying down, I'll just keep a safe distance, cluck to them and swing my lead rope. That almost always gets them up. If it doesn't, I'll pop them on the rump with my lead rope. If that doesn't make them get up, it's either a super docile horse, or he's sick.