This is an interesting thought with an excellent point, and it's one that I've found myself struggling with in the past. What I believe will actually help here is to analyze the nature of the question first, then provide a sort of answer.
When my anxious mind asks me questions similar to yours, it ultimately leads me into a state of confusion and disorientation because we're ultimately unable to answer it concretely. What we look for in these questions, in my opinion, is confirmation or clarity that "allows us" to feel ok or at ease. Knowing that things are a certain way allows us to rest easy and let outside forces take the wheel, so to speak, for us.
That being said, the world is chaotic in that things do function according to the laws of nature, circumstance, and random events, but it's also perfectly normal for us to fall ill, and to echo Chip's point above, this is definitely an odd way of being sick. In this way, we don't need to worry! We are definitely in the real world, but certain things have happened to make us question that we are, and we think a little outside of the box. This is completely ok, and it will heal over time as we allow ourselves to.
What has helped me great amounts with coping with these thoughts is to not buy into them when the crop up. These thoughts are the expression of our anxious mind reaching out to us, asking us to play. As all playdate invitations go, we can deny them. At first, the thought will be persistent, but after repeated denials, the thoughts will crop up less and less. We can also look at these thoughts as visitors entering the room of our mind. If we pay attention to this visitor, it'll sit down in the chair in the room. If we don't pay it any mind at all, it will leave. A visitor will never sit down in a place where it doesn't feel welcome. This is where acknowledging, but not buying into, the thought comes into action. I hope this helps
