I was traveling in my 7 passenger Syncro a couple of days ago (in rush
hour DC traffic). And traffic unexpectedly came to an abrupt halt,
forcing me to slam on the brakes. This worked fine, but for the rest of
that trip, my brakes felt weird...

Essentially after that abrupt stop, the brake pedal went to the floor
and I had to pump the brake pedal to get brakes (I used to do that in
my old beetle, so I adapted with little trouble.)

Later (many hours later on a separate drive), the brakes returned to
normal, i.e. a stomp on the pedal felt normal (no pumping needed) and
braking action occurred as expected.

My thought was air in the  brake line, but it wouldn't have gone away,
would it? And one good stomp shouldn't have resulted in boiling brake
fluid. Nothing else seems out of the ordinary on the Van. Mystery of a
17 old vehicle?