Technically, it's the law. According to part 121 of the U.S. Code of Federal Regulations, no [air carrier] may take off or land an airplane unless each passenger seat back is in the upright position.

No, you cannot lay down during takeoff on any commercial flight in 2026 due to strict international aviation safety regulations (such as FAA §121.311). All passengers must have their seatbacks in the "full upright and locked" position. This is not for comfort, but for emergency egress; a reclined or "flat" seat creates a physical barrier that slows down the evacuation of the row behind you. In a 90-second emergency evacuation scenario, every inch of space matters. Even in "First Class" or "Polaris" pods that offer lie-flat capabilities, the seat must be returned to its upright "taxi/takeoff/landing" (TTL) position for these critical phases of flight. The only legal exception is for passengers with specific, pre-documented medical conditions that prevent them from sitting upright, and even then, they are typically seated in bulkhead rows where their position does not impede the exit path of other travelers.