I've had this since I was a kid.
Usually happens at least once a year in the spring time (grass allergies) and sometimes at other times (from a combination of stress and other things like food or season). An allergist had me use Seldane to treat it back then and that helped me recover faster.
But it's definitely no joke and nobody seems to have a clue how to make it better.
Hot showers are a definite no-no. Take lots of cold showers. Standing outside in the cold helps. Not moving a lot. Soft fabric. No shoes. Coating yourself in Benadryl, soaking your feet in cold water, etc.
I have it pretty bad right now (April-May in Oregon) and have been looking for things online as remedies.
There so many people chiming in about whack stuff. I honestly don't want to hear about finding the cause or drinking nettle tea. I don't think many of these people have the same "class" of hives.
I'm like it's incredibly painful right NOW! and really out of your hands if it's brought on by allergies and I want something that will work right NOW! to alleviate it.
This is a serious thing. You can barely walk as your joints, ankles, and hands swell. Last night I was gritting my teeth walking across the room to let my dogs outside. The first time I got up I just sat back down. No joke. Shivers. All kinds of fun.
I'm trying Allegra right now (what Seldane was) and I think maybe next year I will just start taking the pill beginning of April to see if it will prevent me from getting the rash. So far I only have tried treating it after I get the rash.
I tried Zyrtec last year and it didn't do anything - they just had advertised it as Seldane's replacement. Turkeys!
Last year (and this year) I am taking Diphenhyramine (Benadryl) pills and I have a feeling this works well. Partly because the lotion/spray seems to work well on the hives. So that's about all I've got for remedies.
It still takes a few days for it to clear up, but at least with the pills it seems to cut the time in half. Hope that helps.