"Heavy-headed" is an adjective that describes a feeling of sleepiness or drowsiness, often accompanied by a sensation of pressure or weight on the brain. It can also refer to a state of mental fog or confusion. Some synonyms for "heavy-headed" include lethargic, dazed, groggy, sluggish, and befuddled. Other related words that convey a similar idea include muddled, addled, hazy, woozy, and stupefied. These words are often used to describe the effects of fatigue, illness, medication, or other factors that can impair cognitive function and make it difficult to think clearly or stay alert.