What triggers random anxiety and panic attacks when nothing is going on?

I believe random anxiety and panic attacks get triggered when you are not occupied with something. For example If you drive a vehicle and not steer it, it will go out of course, so similarly with our brains, we have to keep ourselves occupied to prevent unnecessary thinking.

Panic attacks are complex! In general, they are caused by stress, fear, and anxiety. However, they can occur under situations where you do not feel anxious or afraid! For one, physical activity and drugs that increase the activity of your autonomic nervous system can trigger panic attacks. For example, if you go to the gym and exert yourself a lot, your heart rate kicks up and your breathing accelerates. This can bring about a panic attack, especially once you have become overly sensitive to those sensations. Drugs like caffeine can have a similar effect on your body; they increase your heart rate and can bring you to an altered state of mind similar to that of exertion. The bottom line is that if you have a history of panic attacks, you will be hypersensitive to anything that increases your heart rate, changes your mental sharpness, causes stomach discomfort, etc.

For me, when nothing is going on, my anxiety tends to be triggered by my thoughts and the things that go through my mind, whether it be something I'm stressed about or a memory that makes me upset. Actually, anxiety for me tends to be heightened when nothing is going on because the absence of a distraction gives my mind more freedom and time to think and wander, which eventually leads to anxiety and in some cases an anxiety attack.

For me, it's the thought that I've missed something. I may feel like nothing is going on, that I have it all under control, but then I might get the sneaky feeling that I missed something I desperately needed to get done, and start feeling anxious again.

If there doesn't seem to be any cause for being anxious or on edge (i.e. a big crowd you have to speak in front of, or a bear in your backyard) then the anxiety and panic COULD (not certainly) be caused by Generalized Anxiety Disorder. If you can't seem to identify what the worry is, and have trouble concentrating, and falling/staying asleep, talk to a professional for their opinion. Don't self-diagnose.

Random anxiety can be brought on by a number of things that we may or may not be acknowledging consciously. I call it the "snowball effect" when all the small stressors roll together and become a large one that can be overwhelming. This can be the cause of anxiety and panic attacks as well as other things.

There may not be anything going on at the moment, but instead there may be some thoughts that trigger these anxiety or panic attacks.

Sometimes it's your subconscious mind acting up - it may sense danger that isn't there, or feel uneasy about this environment. Try keeping a mood journal that details your emotional journey, this way you can manage and understand your condition.

I think a fear that things are too peaceful at the moment and the worry that something will come in and disrupt that can cause anxiety even when it seems like nothing is going on.

Anxiety/panic attacks are due to chemical imbalance in brain. In that case, even minor stressors are causing you to feel severely stressed. You shouldn't feel guilty about having them, but you should learn to manage your anxiety levels so you can live a better and more fulfilling life.