Since you would have had lunch with him, have your mutual friends get his number for you.
You call, explaing what MAY have happened and ask him to lunch.
Edit: We dish out advice all day long to strangers asking for advice from other strangers. Why can't WE figure out what to do when it happens to US??
Couldn't agree more. The simple solution is staring you in the face. I doubt he'd spazz if you actually went through the trouble of finding out his number and actually called him. Especially if you give him your number again and he sees that he switched some numbers or got a digit wrong or the wrong area code or whatever. Unless he's unstable, then he'll spazz anyway.