Hello thanks for the query. \rRash developing overnight can be either due to insect bite or an allergy. \rAs you mentioned there is no itch, insect bite can be ruled out. \rMost probably you have developed an allergic reaction to the linen. \rIt is quiet common and is called as cloth dermatitis. \rApply a mild steroid lotion like hydrocortisone and take anti histamine tablet. You will be fine. \rLet me know if you have any other doubts. \rThank you.