Thank you for contacting HCM with your health care concerns. You notice a rash each evening upon sleeping and then resolving in the AM upon waking. This seems to me that you have an allergy to something in you bedroom or in your bed. The most common allergens would be house dust and the mattress is one of the worst offenders for house dust. I recommend changing sheets frequently and actually vacuuming your bed with each sheet changes. You could also take an antihistamine before sleeping to reduce the rash.