From terminal +‎ lucidity.

terminal lucidity (uncountable)

1. A rare, mysterious phenomenon when someone with a severe neurological or psychiatric condition (like dementia) experiences a sudden, temporary return of mental clarity, memory, and personality just before death, allowing for clear communication and recognition; appearing one's old self for a brief period before passing away.

• terminal rally
• rallying
• rally
• pre-mortem surge
• energy surge
• surge
• end-of-life experience