One of the leading naturalistic attempts to account for Jesus’ death, empty tomb, post-mortem appearances, and the early proclamation of the resurrection is that the disciples had individual and group hallucinations. In this case, the New Testament authors would not have meant that the resurrected body of Jesus was physical. But is that what they recorded?
We’ll look at the words for 1) resurrection, 2) body
Here’s a quotation from my friend Eric Chabot, from his blog Think Apologetics. He explains why Paul’s use of the word “resurrection” to describe what the other witnesses saw means bodily resurrection.
The two words are used for resurrection in the New Testament “anastasis” (rising up) and “egersis” (waking up), both imply a physical body. Furthermore, the use of the word “opethe” (the Greek word for appeared) shows the Gospel writers did believe that Jesus appeared physically. “There you will see (opethe) him” (Matt. 28:7); “The Lord has risen and has appeared (opethe) to Simon” (Luke 24:24). When they used “opethe” here, it means that He appeared physically to them.
OK so all the words they used for resurrection imply a physical body.
But what about the word for body. Do they imply a physical body?
So when Paul gives his list of appearances in 1 Cor. 15, the issues becomes whether the appearance to him is the same as it was to the disciples. There is no doubt the post resurrection body of Jesus (after the ascension) had to be somewhat different than the body the disciples saw. Also, whenever the New Testament mentions the word body, in the context of referring to an individual human being, the Greek word “soma” always refers to a literal, physical body. Greek specialist Robert Gundry says “the consistent and exclusive use of soma for the physical body in anthropological contexts resists dematerialization of the resurrection, whether by idealism or by existentialism.”  Furthermore, in N.T. Wright’s The Resurrection of the Son of God shows that the Greek word for resurrection which is “anastasis” was used by ancient Jews, pagans, and Christians as bodily in nature.
What about the nature of Paul’s appearance? Was that a hallucination, or seeing some objective reality? Did the people with Paul see or hear anything?
Eric Chabot writes this in another place:
The Bible says, “they heard” the same voice Paul did ” (Acts 9: 7). But they “did not see anyone ” (Acts 9: 7). Notice Paul was physically blinded by the brightness of the light. One way or the other, the experience involved something that was external to Paul. It wasn’t something that was the same thing as a vision that Paul talks about in 2 Cor. 12:1. Furthermore, the phrase “he let himself be seen’” (ōphthē , aorist passive,), is the word Paul uses in 1 Cor. 15:7 to describe of his own resurrection appearance as the other ones in the creed.
Paul didn’t get a bodily resurrection appearance, but he got an objective appearance that people nearby could see (as a bright light) and hear. His appearance, coming 20 years after the appearances to the disciples, should not be seen as overriding their appearances, which were appearances of the bodily resurrected Jesus.
If you want to read something a little more challenging, I found a paper from the Evangelical Theological Society (ETS) from their journal, where it talks more about soma and anastasis. If you want a bit of a challenge, download the PDF and read it. It’s by Kirk R. MacGregor and the title is “1 Corinthians 15:3B–6A, 7 And The Bodily Resurrection Of Jesus”.