@Barklessdog:
Hair standing on the back is a warning sign. She's testing her pack order. Do not let her play this game. Be in control, stop her by getting a treat and making her sit for it.
Start enforcing your alpha at anytime, even with puppies. You do this by controlling her behavior, not her controlling yours.
I don't agree. Pilo-erection (or hair standing on end, or ridgie, or whatever you call it) is a sign of arousal, not aggression. Of course an aggressive dog IS an aroused dog so you WILL see it then…but it doesn't mean the dog is feeling aggressive. You can see it when a dog is excited in play, or afraid and feeling like they might need to flee, or when a dog is deciding if a situation is dangerous.
My guess is that your dog is really confused when you lie on the ground, and she is aroused because she is trying to sort out the situation. If you do it frequently, and don't make a big deal about it she will become conditioned to it, and won't think of it as strange anymore.
Think about it this way...if you were walking down the street and saw a person lying face first on the sidewalk, you would be alarmed, right? You might wonder if you should run for help, or run away, or run to them to pick them up, most people would be conflicted in that situation, and so is your dog. Your conflicted emotions wouldn't indicate that you felt superior to the person lying on the floor, or that you were about to attack, right? But if you walked over and the person grabbed you, you might attack. Your brain is waiting for more info on how to proceed...so is hers