Urticaria often worsens at night due to natural histamine increase, lower cortisol levels, and increased body heat under blankets, which makes itching feel stronger during sleep. Triggers like stress, heat, dust mites, pet dander, or bedding materials can also cause nighttime flare-ups. You should see a doctor if hives last more than 6 weeks, keep recurring, or come with swelling, breathing issues, or other unusual symptoms, to rule out allergies or chronic conditions.