This is not a medical advice. Take it at your own risk.
The seed is toxic. There were studies that use the seeds to kill cancer cells.
Cherimoya seed takes a few weeks to bud out. Food you eat will take a day or two to come out. For a day or two, I don't think the seed will grow and poison you. Just like watermelon seeds, I think it should come out whole, not digested. I don't think one seed is potent enough to do any serious harm.
What if it stuck in your appendix? That I don't know.