Are all feelings created by thoughts, really ?

What about this: I am walking peacefully in calm surroundings when a man comes storming and shouting out of nowhere.
I am immediately startled – it seems to me that this is a reflex, because I had no time to think anything  about it !
And luckily I do not have any heart problems, otherwise it would not be impossible to have a heart attack right away.
How can the model explain this ?

Thank you !