Child worried they’re not real

My son will be 10 years old in about a month. Tonight he started asking my husband and I how we know if we’re living in reality. He has asked this before, and we’ve told him that we also wondered that when we were his age. He ended up sobbing because he is so worried about this. It’s concerning, and I’m wondering where this is coming from. He does play some games on his VR headset. Any chance this is causing the confusion? Have any other parents had this issue?