What Does Non-itchy Skin Rash On Arm After Sleeping On It, Indicate?

Hi my husband slept on his right arm last night, when he woke it was completly dead, this recoverd as normal but he has a red rash down his forarm and on the back of his hand, its not itchy or raised but it may be a little warmer than normal. the rash has now been there for about 16 hours and hasn't changed but has got slightly smaller.