For some people, GB pain and discomfort does occur on the left side. It's not a typical symptom, but it does happen. If you believe you're having GB issues, talk with your doc.
If anything was spasming on your left side it was very likely your stomach. Why it was spasming is another question altogether. Gallbladder issues could possibly cause digestive delays, making the stomach work harder. What happens when you overwork a muscle? It tends to twitch. If there are other symptoms--heartburn, bloating, pain, nausea--then the twitching could be indicative of a motility issue and should be looked at by a doctor.
Of course, it could also be gas.
@mammo: Actually, the liver isn't on the right. The bulk of it is on the left, but it's huge, so it spills over to the right.
Image:
http://www.nlm.nih.gov/medlineplus/ency/images/ency/fullsize/8850.jpg
Your gallbladder is on your right side, the liver to the left. Sorry, but this is not something I'm aware of. Best of luck to you.