Hi, My Son Is 13 Years Old And Has Been

Hi, my son is 13 years old and has been experiencing episodes of a very tight chest. He starts to feel like his lungs aren't expanding and then he gets very nervous and his heart races. Strangely, it seems to happen often while riding in a vehicle. Until last night when he had a pretty bad episode at home for about 45 minutes. I tried to tell him to lay down and relax and he said it hurt and his chest felt like there were bricks on it when he laid down. He used his inhaler but it didn't seem to make a difference. I put my ear to his chest and noticed his heart was beating pretty fast. He eventually fell asleep. Today I called home to check on him from work and he said it is much better but still not "normal". Any ideas what could be causing this?