Hi, long term anxiety/severe depressive episodes person here.
I wanted to say that it seems COVID can affect a lot of people's tummies. The stomach and the brain are linked by a large nerve that lies along the bottom of the stomach. Any sort of stomach upset can trigger anxiety.
I would expect what you are suffering from is acute anxiety brought on by COVID. It is awful when in the stage of peaking anxiety but it doesn't last. We can't stay in a state of extreme anxiety all the time, it's just unsustainable.
You need to eat, whether you feel you can or can't. Going hungry worsens anxiety, it just reenforces to your brain that there is something to be anxious about. Low blood sugar can also mimic anxiety symptoms. Eating is non negotiable. Eat whatever you can, as often as you can, such breakfast bars, Ice lollies, smoothies, soup. A sip of something is better than nothing. A mouthful of something is better than nothing.
The feeling of not really being here comes from adrenaline from the anxiety changing your vision. It's a self protection feature that is supposed to allow is to see the quickest escape route when in danger. The best way to stop this, is to work on lowering your anxiety levels. You can do this by not fighting the anxiety. It feels awful but instead of trying to escape it and distract from it, let it do what it's doing and try to remain calm. Basically your anxiety is happening because it thinks something is dangerously wrong. When we stop doing our usual routine, we just encourage it. We need to do what we usually do, to get the brain to realise there is no danger and turn off the anxiety.
So eat. You can, it's just anxiety making you think you can't. If you are able, try to get outside in your garden and gently walk around it. Exercise, no matter how little, helps calm anxiety. Speak to people on the phone, friends, family etc. Go to bed at the same time even if you don't sleep for hours. Avoid anything anxiety triggering, such a googling symptoms, reading the news, listening to emotional music and so forth, don't put negative things in your brain for the anxiety to feed on.
This will pass. It is not permanent, it will go.