If the earth's gravitational field collapses for "a few seconds", what worst or best can happen?

How's it going to collapse?
The worst thing would probably be the fact that water will no longer be confined to rivers, seas etc. I would expect largescale flooding when the gravity was turned back on.

Apart from that, everything that wasn't bolted down would float around a bit. No biggie.

Some other possible consequences:

1. Airplanes in flight would be flung up by the sudden elimination of their weight - for those few seconds the wings would continue to provide lift, but with no weight to offset the lift force the plane would move up at approximately 1g acceleration.

2. The atmosphere would suddenly rush skyward - again acceleratoing at about 1 g. Within a few seconds the updraft velocity could reach a pretty high velocity. If the condition lasted too long we could lose a fair amount of the atmosphere to space. Also the atmospheric pressure at the earth's surface would fall - it may quickly become difficult or even impossible to breathe . Then when gravity switched back on the down draft might knock everything flat - if Capuchin's flood hasn't gotten them already, the winds just may.

3. All of earth's satellites would be thrown into different orbits. I doubt that any of the geo-stationary satellites would be in the right place once the gravity came back on.

4. Anyone who had the misfortune of bouncing on a trampoline or diving board just as the gravity switched off would be in big trouble.