Paul’s conversion has natural explanations: guilt, a seizure, heatstroke, a psychological crisis. Acts describes a light and a voice, which sounds like a vision, not a bodily encounter.

Any of those is possible in the abstract, and Paul’s experience should not be pictured as identical to touching Jesus in a locked room. What the natural explanations struggle with is the aftermath. Paul did not merely feel differently; he went to Jerusalem to check his understanding with Peter and James, adopted their specific claims about the resurrection, and held to them through beatings, prison, and eventually execution. A guilt-driven hallucination would not be expected to match, in content, what the Jerusalem apostles were already preaching before he arrived.