Daniel Dennett, one of the four most prominent “New Atheists,” is no proponent of the Resurrection of Jesus Christ. The hallucination theory to explain Jesus’ post-resurrection appearances is no longer held by many scholars. Nevertheless there are exceptions to this, including Gerd Lüdemann (detailed further here). In Consciousness Explained, however, Dennett says on page 7,
Another conclusion it seems we can draw from this is that strong hallucinations are simply impossible! By a strong hallucination I mean a hallucination of an apparently concrete and persisting three-dimensional object in the real world—as contrasted to flashes, geometric distortions, auras, afterimages, fleeting phantom-limb experiences, and other anomalous sensations. A strong hallucination would be, say, a ghost that talked back, that permitted you to touch it, that resisted with a sense of solidity, that cast a shadow, that was visible from any angle so that you might walk around it and see what its back looked like.
(See the full argument here; go to page one if it doesn’t open directly there) Based on Dennett’s analysis, then, hallucinations cannot explain the events in Matthew 28:9-10, Luke 24:13-48, John 20:24-28, or John 21:4-19.
See Gary Habermas for more on hallucination theories.