have a case of (something)

1. To be stricken by a bout of some illness. My grandfather had a case of the measles when he was a child that left one of his legs partially paralyzed. Turns out, I had a case of pneumonia and didn't even know it because I cough all the time! If Lily has red spots all over her skin, she might have a case of chicken pox.

2. By extension, to experience an occurrence of some emotional condition. Liz usually loves to sing for an audience, so I think she's just got a case of jittery nerves. I don't know what's got me so down. I've just had a case of the blues since I woke up. Stop telling each other such silly things. I don't want you to have a case of the giggles in the middle of church!