My brother (an adult) said he woke up several weeks ago in the middle of the night with a rach and hives under his arms and in the crotch area. He hasn’t done anything different lately that would contribute to this condition. He says he sleeps with a heated matress pad which he keeps set at #2 setting. Could this change in temperature while he is sleeping cause this? Nothing in his diet or lifestyle seems different. Ever had anything like this?