Now I've never needed a root canal, but I've had a couple of pretty painful cavities that were very close to reaching the pulp! In my case, the pain wasn't what I would consider severe, but the sensitivity to sugar was excruciating! I could eat a piece of chocolate and be in tears!
Since your x-rays didn't show any questionable areas, I'd say you're just fine. My dentist can pick up even the tiniest spot of decay via x-rays.