TMZ obtained footage which begins moments after the fall -- Reid is sprawled out on the ground next to the bike ... while her equally hammered female friend is slumped across the top of the downed vehicle.

Several people try to help Reid off the ground ... but she struggles to pick herself up.

Once the two women get on their feet, both drunkenly sway back and forth in what seems like an epic battle to stand still and compose themselves.

Eventually, the two women wobble over to a nearby yacht ... and board the vessel like they had been there before.