Anybody ever had a side-stitch while swimming?

Yesterday afternoon, I set out to have a nice long swim. At about 500 yards, I started developing a side-stitch. I thought it was pretty weird, 'cause I've never had one while swimming before. However, I figured it'd be good practice to 'swim on' since I couldn't see myself stopping for one in a race, so I'd use it as a good practice session to push on thru. It continued to get worse and worse until at about 800 yards, it was borderline unbareable... I had to stop for a few minutes to let it go away. At one point, I don't think I could even get out of the pool it hurt so bad. It eventually subsided enough to put in another 200 yards and call it a day at 1000 (far less than I set out to do), but how weird was that? That's never happened to me before - I've never even heard of a side-stitch while swimming.... Have I just been lucky so far as this is common, or is this a first? Anybody?