When the dog vomits

Sometimes my dog vomits with for no apparent reason. She doesn't even make any noise, we just find or accidentally step in a vomit puddle... It never seems to be because of food, she tends to do this when she's stressed or bothered about something. Sometimes I wonder if she does this on purpose. She has this habit of peeing/pooping in the wrong place when we don't give her food or leave her alone longer than she's used to. Also, sometimes she starts choking and when we run to help, she stops immediately. It's like she does it for attention.