Freezing in May?

Came back rather quickly with an ice cream dreaded headache. Gnarley. Waves were like 4 feet, clean and looked fun. Looked like a fun morning & I was ready to surf for at least an hour or two. Well I lasted like 20 minutes. All my muscles froze up, could hardly stand on the board to get my last wave in. BRR & WTF! Shouldn't May be warm?