During a recent trip in a Finnair A350, a couple traveling together was occupying 1 row of three Economy Comfort seats. During the 12 hour flight, one of the couple stretched out on the seats, the other one on the floor in between the seat rows, leg room being sufficient to allow this.
A flight attendant was overheard stating that sleeping on the floor was not allowed due to safety regulations. What safety regulation would prohibit this?
update
During cruise condition, no Fasten Seatbelt sign. EASA regulations. Yes you're out of your seat but we're allowed to walk around aren't we. Where is the hard, written, safety regulation?