An interesting question to think about is what to do next if you believe you have fallen prey to a spiked beverage ... or food.
It could be helpful to have an 'exit' plan, with some consideration about how to handle sudden incapacitation in an unfamiliar place.
On one occasion - decades back, I and a couple of friends stopped at a roadside franchise food stand for a snack of 'fish-burgers' on the way to an afternoon excursion with a group on a tour bus. About the time we reached the group, the three of us began to feel lightheaded and rather dizzy. Not long afterward we commenced to see the world with more colors than usual. Fortunately the bus tour placed little demand on us.. other than climbing in and out of the bus.. because we were pretty loopy for the entire 4 or 5 hours.
That incident worked out harmlessly enough - was rather interesting, in fact - but it put that category of scenarios in sharp perspective. The conclusion - unverified - was that a bored young worker at the food stand had chosen to play a prank on us, possibly by adding something to the abundant 'tartar sauce' served on the fish. Under other circumstances - alone, foreign place, stronger effects, etc., it would have been truly terrifying.