With a mental overreaction, you are telling yourself through your mental processes that you are in grave danger when you are not.
You might be thinking “I don’t tell myself anything” “I wake up with anxiety, I haven’t even thought of anything” or “when I worry or think of bad things that could happen, they are possible, it is not irrational”
All I can say to these thoughts is that if you are having a physical “life or death” reaction to something that you are simply thinking about, and you are not literally in “a life or death” situation, then it is, in fact, an overreaction.
One of the scariest things about anxiety is the physical symptoms, and understanding what is going on inside your body is a tremendous aid in reducing that anxiety. If you are experiencing a “life or death” feeling, then your brain will look for an explanation when the symptoms arise. If there is no lion about to eat you, then the brain will come up with something else, for instance, “my chest is tight, there’s a pain, I can’t breathe, it must be a heart attack or COVID19”, “I feel dizzy, I can’t think or focus, it could be a stroke or tumour”, “ I’m sweating and trembling, something serious is wrong with me”. There are many other, what appears at first glance to be plausible, explanations. We can get even more carried away and think “was it that text I sent yesterday, have I offended her?”