Since you mentioned you are on a vacation, I would assume that you bought a return ticket. ie. SFO-SIN-SGN-SIN-SFO.

If you are a no show for SIN-SGN, the rest of your ticket from SGN-SIN-SFO may be cancelled.

So unless you don't need to return home, then you'll probably want to take this into consideration before buying a separate ticket.

That's what malmostoso meant.