Possession - after her husband and brother-in-law are involved in a head-on collision, a woman is stunned when her husband appears to have been transported into his brother's body.
An alternative synopsis for this would be: a woman attempts to justify acting on her nascent desires for her douchebag brother-in-law after her simpering, saccharine husband ends up in a coma. This is overly sentimental tripe, but mildly amusing when you see through the supposed storyline to what's going on underneath, which must be way more obvious than they'd planned.
Also, there must be a million films called Possession, or The Possession - I keep finding new ones. Must be a scunner if you're trying to have a conversation about one of them.