So my little sister (13) tells me that for years she's had this thing where a couple times a month, out of the blue she'll suddenly get this feeling that there are people laughing at everything she's doing. Even if she's alone she'll still feel like people are ridiculing her. She says that it lasts 20 minutes or so and then it's gone. It's hard for her to describe but she says that it makes her miserable to feel. I love my sister immensely and want her to be happy, and am also pretty confused by this. Any idea what it is or what might be causing it?