I’m going to be relying very heavily on what I learned during my own therapy here. I know that your problems are different to mine, but as far as I know the following advice can be applied to just about anyone, so hopefully this might serve some use:
Problems such as depression, anxiety, phobias, etc, tend to be created for a good reason. They’re a part of our innate thread response systems, and the behaviours these emotions and fears lead to are intended to protect us. Anxiety leads us to avoid situations that we believe pose a threat to us in some way. It’s just our body’s way of telling us, “You’re taking a big risk, be careful”, or even just flat out: “You shouldn’t be doing this”. Anxiety is generally a useful thing, but for some the threat response system becomes a little too sensitive, and it becomes a problem.
Our threat-response systems are affected by a multitude of different factors. Your upbringing plays a very large role in how you respond to stress, as do any traumatic events in your life, and it’s largely just genetic. However, it’s not something that’s completely beyond our control. The way to beat it is to start challenging the unhelpful beliefs that are reinforcing your mental state.
Here’s an example from my own experiences:
I believed I was generally unlikeable and that I’d never be able to really connect with anybody (more of a depression issue than an anxiety issue, but the principle still applies). I identified this belief, and really forced myself to think about it. I reflected on my experiences over the last few years, and realised that I’d actually made quite a lot of friends (by introvert standards, anyway). I’m also very close with some of those friends, and we’ve trusted each other with some pretty personal information over the years.
The reality was that my belief did not hold up. That belief had been leading me to feel depressed, which in turn made me act moody and short-tempered, which in turn caused me to regularly start arguments with my friends. Whenever that happened, I would reflect on the argument, think, “I really am unlikeable”, and the cycle would repeat. Meanwhile, I wasn’t paying attention to all of the good experiences I was having with my friends which directly opposed my belief.
I imagine something similar is going on for you. The solution is to really think it through: What scares you about it in particular? What’s your emotional response when you think about it? (like, just fear, or are there other emotions mixed in?) What do you think the results will be if you do go out in public? Is this causing any specific behaviours or physical responses? (You already mentioned feeling tense, getting cramps, feeling nauseated, so just more stuff like that). It’d probably help to write it all down somewhere. Maybe even draw it up in a cycle like the one I described earlier.
Once the problem is identified and understood (which may take more time and effort than you’d think), you can start challenging it. Just go outside and take the risk. See it as an experiment. Afterwards, try comparing your experience to everything you’d written down beforehand. Were the results comparable? I imagine you’ll find that it won’t be as bad as your fears suggested it would be. If you repeat this over and over again, each time reflecting on whether or not your beliefs held up, eventually you may be able to make some progress towards removing it altogether. Start slow though.
Oh, and it may be a good idea to look into getting some medication if you haven’t already. I saw in your earlier post that you suffer from depression as well as anxiety, and there are quite of a lot of drugs that reduce both (sertraline, my own medication, is primarily prescribed for depression but also serves as an anti-anxiety drug). It’s rare for medication to solve the problem entirely, but it often does help.
So yeah, good luck tomorrow, and I hope you start feeling better soon.