Surely if you need to sleep, you will sleep - whether there is daylight, loud music, foodly aromas, turbulence or whatever. It is only problematic if you merely want to sleep.

I shall be taking my first F flights over Christmas to Thailand (not on BA). The outbound leg leaves London at 2135 and arrives at 1555 so it will probably be dark most of the way. On the return leg, though, we leave BKK at 1235 and arrive at FRA at 1900 - this doesn't coincide with sleeping time in either Thailand or Europe. Is it reasonable to assume we'll be "allowed" the shutters up during that flight?