Confusional arousals — sometimes called sleep drunkenness — are brief episodes where you wake, or partially wake, in a state of significant disorientation: slow to respond, confused about where you are, sometimes irritable or behaving oddly, with patchy or no memory of the episode afterward.
What's actually happening
They occur when your brain gets "stuck" partway through the transition out of deep non-REM sleep — part of your brain is awake enough to move and respond, while other parts, particularly those responsible for full alertness and memory formation, are still lagging behind. This is different from a nightmare or panic attack: there's usually no fear response, just confusion and grogginess.
Who experiences them
Confusional arousals are extremely common in children, who often grow out of them, and also occur in adults, particularly when sleep-deprived, waking from an unusually deep sleep, or being woken abruptly during the deepest part of the sleep cycle. Shift workers and people recovering from significant sleep debt are especially prone to them.
What they look like from the outside
Someone experiencing a confusional arousal might sit up and stare blankly, mumble something that doesn't quite make sense, or respond slowly and inappropriately to questions. Unlike sleepwalking, they usually stay in or near the bed. They're generally harmless and resolve within a few minutes, though the person having one rarely remembers it clearly.