The House M.D. episode in which House temporarily loses his memory is titled “House’s Head.”
“House’s Head” is the first part of the season-four finale and originally aired on May 12, 2008. House wakes after a bus accident with a severe headache and no memory of several hours, during which he believes he saw a critically ill passenger who needs help.
The episode uses fragmented recollection, hallucination, and investigation to make House reconstruct what happened. Its mystery continues in the second part, “Wilson’s Heart,” which reveals the identity and fate of the patient House was trying to remember.
The title is sometimes confused with “Locked In,” another episode involving altered consciousness and diagnostic uncertainty. However, “House’s Head” specifically centers on House’s amnesia after the bus crash and is the episode that begins the two-part finale.