Exploding head syndrome (EHS) is a condition that falls under the category of sleep-related disorders. Those affected by EHS experience auditory hallucinations that are described as loud noises — they might sound like a bomb exploding, a gunshot, or a cymbal crash — occurring just before falling asleep or upon waking. The sound is vivid and real to the person experiencing it, but it is completely internal; there’s no actual sound being produced externally.