Totally Freaked

Tim (my dog) totally freaked me out! We were just sitting out back, he was sitting beside me then all of a sudden he's front legs started to give out on him then his hind legs. His whole body stiffened up and he just lay there on the ground. After a min or two he seemed to gain some control back and waddled out into the yard unable to walk strait. Making it sideways to the middle of the yard and collapsed. I followed him and rubbed his belly to keep him relaxed. He stayed disoriented for then next 10 minutes or so and now he seems fine. I feel so helpless when things happen to the dogs.