Does hideous laughter make a flying foe prone and cause the foe to fall?

A witch that’s using the flight hex to fly 20 ft. up in the air fails her saving throw against my halfling bard’s hideous laughter spell. The spell says that an affected creature

collapses into gales of manic laughter, falling prone. The subject can take no actions while laughing, but is not considered helpless.

Does the witch become prone in the air? Does the phrase take no action mean the witch falls to her death, grappled and subsequently slain by her own foolishly placed black tentacles?