Why do panic attacks sometimes come out of the blue for no reason?

It may seem that they are out of the blue but that is only to the conscious mind. There may be underlying reasons in our subconscious causing these panic attacks. These underlying reasons could be anything from hidden stress, an unknown fear, etc. Regardless of the cause there is no out of the blue for a panic attack it only appears that way.

Panic attacks usually have triggers, maybe your trigger is unknown and you haven't realized that you have an unknown trigger.

Its because the person had an earliar experince with such situation .. when it occurs again the human mind tends to react the same action it did before .

Because that's the definition of a panic attack. They are triggered by something, it all works by triggers, a smell, a sound, a sensation, and this trigger or you can say switch, turns on the panic attack, like a TV channel. One small thing brings up trauma. It's like when you take notes in school, your goal is to write in key words to remember what you learned, not to write word for word. So memory words by small reminders that are attached to large amounts of information, memories or events. It's how the brain works. Use this to your advantage.

Panic attacks are usually triggered by something, but it can be hard to tell what it is, especially when it's a subtle trigger.

Personally for me, sometimes. I just have "off days" where my panic attacks will happen over something that I usually would react normally to. So I can't say it's out of the blue, but sometimes it doesn't seem as warranted.

Our brains believe you are in danger at the moment and that is why they pop out of the blue. There is a more scientific explaination for this though!

Panic attacks sometimes come out of the blue because the mind and body is reacting to a situation that triggered severe anxiety. Some people are unaware that they are experiencing a panic attack until they are already in the middle of one.

In my experience I tend to overthink without clarification. I need to learn more techniques in coping and just chill.

Panic attacks appear more in times of stress but small things can set them off too especially if I've been holding feelings in. And sometimes they just happen for no reason