The Resurrection appearances were not hallucinations or visions because:
The evidence shows that the experiences were real, tangible, and not subjectively generated.
In other words, Jesus really appeared to them!
[1] The Case for The Resurrection, Habermas and Licona, pp. 105-119. Also see Evidence That Demands a Verdict, 247-255. These two books cover a rebuttal of the hallucination theory in great detail.