A person who is straight when awake, but in dreams have sexual fantasies about others who are the same gender as him/herself. usually happens when stressed, having doubts about a relationship or after watching a chick flick/action movie.
Sarah: Hi john.
Sarah's BF John: hey sarah have any cool dreams lately?
Sarahs thoughts: dont say anything about the dream you had last night about mary....
John: oh okay.
Sarah's thoughts: i knew i shouldn't have watched "jennifers body" last night... damn megan fox turning me into a Diurnal Bisexual..