I had a panic attack last thursday morning but I dont know why?

Hey I have a question I had a panic attack last thursday morning and it is the first time it has happened to me, it had happened after I woke up and went to take a shower, after the shower I felt dizzy, I was breathing heavy like I just finished running, I almost fainted, but I went sittin in the living room and the panic attack went away. Why did I have a panic attack?