A sweater can make you feel sleepier for a few simple body reasons: 1. Warmth signals “rest mode” When your body gets warm, your nervous system shifts toward relaxation (parasympathetic mode). That’s the same system that turns on when you’re cozy in bed—so your brain reads “safe + warm = time to rest.” 2. Body temperature affects alertness Your brain stays most alert when your core temperature is slightly cooler. A sweater can raise your body temp just enough to reduce alertness and trigger drowsiness. 3. Comfort lowers stimulation Soft, snug clothing reduces sensory input. Less stimulation = less mental arousal = more sleepiness. It’s why people get sleepy under blankets even during the day. 4. Blood flow changes Warmth causes blood vessels to widen (vasodilation), which can slightly lower blood pressure—another subtle sleepy signal. 5. Psychological association Your brain likely associates sweaters with evenings, indoors, winter, couch time, or rest. That conditioning alone can ...