Well, that is a real question. But that is not my argument. I point out instead:

1. The big arguments used to disprove God also disprove your own existence, as they disprove the existence of sentience.

2. There are religions centered on sentience, and who equate God with sentience.

3. It is manifestly absurd to believe one is not sentient just to hold to physicalism.

You can't ever be certain about the nature of reality but you can be damn sure reality is not solely square. It is important to look to, and study, the circle as well, instead of pretending it does not exist.