I don't think you should fold. First of all, only two cases your are clearly underdog: Vs AA, and here there isn't nothing else, and Vs KK and in this case you have the A. In the other cases the worst you cang get is a flip (vs other pairs) and to be clearly the best hand(Vs the rest of the hands).
Obviously he wouldn't 3bet with nothing that don't be really strong, but consider the in 6-max the players are very aggressive and you might be facing starting hands like AQ, AJ, 99++. And taking into account the aggresivity of the villains in SH and the worst situation (AA or KK, just 6 combinations because you have AK) you might be facing a flip vs a pair(QQ--). also take into account that incluiding the most tight villain would go allin preflop with hands like QQ, or JJ in SH. then you can't assume tha you're very underdog to fold.
I think would be good to see the board.
Excuse my english, it isn't still the best.