Stress and anxiety can cause a lot of physical symptoms such as headache, nausea, vomiting, stomach ache, diarrhea, fever, aches and pains, sharp shooting pains, coldness, and the list goes on.
Being stuck in an elevator. Well when thinking of a dream from a psychological standpoint, you have to take such things literally. An elevator moves up and down, but your friend is stuck in one. I would say she isn't very happy at the moment in her life and feels like she is getting no where. This obviously bothers her a great deal and causes her much stress because when she thinks about the dream, the connection to the dream and her subconscious upset over this "stuck" time in her life causes her to literally feel ill. Was she desiring to move up in this elevator or get off? Because if she wanted to move up, perhaps she has high aspirations for herself in life and she isn't reaching them as she had dreamed. Maybe she wants a promotion or a better job and can't seem to get it. If she wants off the elevator, than there is an additional feeling here, or being trapped. She may feel forced to do things she doesn't want to. She wants to leave/stop and experience a change and can't.
Does she have an elevator in her apartment building or workplace? Because depending on where she tends to ride elevators may also hold the key to where in life she feels trapped/stuck.