Physical anxiety is adrenaline/cortisol(?) rushing through your brain and it can be triggered by infection, hormonal imbalance and anxious thoughts. The result is the same though regardless of the source!
Infections and hormonal imbalance will send an emergency signal to the brain to correct the trauma and, thus, if your imbalance is strong, and particular volatile like in perimenopause, you will have a strong reaction.
The difference between anxiety and depression was well explained earlier about the past and the future. When we are anxious we are desperately trying to control a situation and stop something bad happening, hence all the adrenaline pushing us to act - the fight or flight response. Once we feel we can no longer do anything about the situation we mentally ‘give in' and the adrenaline plummets and we feel numb and stuck.
Also if anxiety goes on for long enough without resolution, the brain will automatically trigger a depression to bring the heart rate down and protect the person from imploding with stress!
When anxiety is thought driven, for those who mentioned it here, yes it is hard work to try to change your old habits of negative thinking as habits come from the subconscious and are formed to make our lives easier, so will always be your default until you change your habits - very much like phobias and sleep patterns.
It's not about changing negative thoughts to positive thoughts as these are just as exaggerated and untrue. It's about changing them to rational thoughts, as in instead of “I can't stand it, I'm probably having a heart attack†or the positive exaggerated “I don't care, I'm happy†you say “I can stand it (as I actually have been), I'm not sure what is happening but I'll get checked by the doctor and find out what needs to be done, otherwise it will mean I'm fine and so no point in worrying as I don't have the facts.†Or a simple “things will work outâ€.
The more you consciously override your irrational thoughts with rational ones they eventually will become your new habit and you'll naturally be calm. You do have to put the work in first though which is one of the reasons clients don't always want CBT! It's one of the therapies that are completely in your control though and can be self taught in the same way your thought-driven anxiety was self taught!