DH night illness - swelling, crawling sensation, nausea

[Fluffyogabunny]

A plea for help. My DH has had strange symptoms for about a year. It comes on him quickly and sometimes wakes him from sleep. He feels nauseous and has a crawling feeling under his skin. His hands and feet swell and he feels hot in general. His doc tested for a few different things such as shellfish and all came back negative. They prescribed antihistamines which he now takes if he has an attack. It's hard to know if they help as he recovers within an hour anyhow. He has pushed for further allergy testing but it takes months...already waiting three. He had a very bad episode last night. He seemed dehydrated and had been very stressed the previous day. Could it be anxiety or dehydration? Just worried something else is underlying. Otherwise he's in good health. Eats well and exercises. Any ideas would be great as the docs are just not helping to get to the bottom of it. Many thanks