Weird! I found this site informative: http://www.everydayhealth.com/specia...ves/index.aspx

I had hives every evening for awhile but it turned out to be my cat; he'd been an outdoor cat but got old/not feeling well so would sit on my lap. What are you doing an hour or so before you go to bed? Anything changed there? Did you try going to bed at different times to see if it shows up the same time or in the same circumstances?