All credit to you for wanting to share your 'freaky' experience with others. I always reckon, never be too proud to admit mistakes, and that way we can all learn from it .......
Pedals, jumping up and down ? Sounds like it might have been nosewheel shimmy to me....... what speed was that at ? If so, best to keep the weight off the nose and bring the controls back.
Braking would only make it worse.
I wouldn't have thought that overtrimming would prevent your nose from lifting. Sure, it could markedly increase the amount of back pressure you require, but my guess (and it is only a guess) ... (as it has happened to me before) is .... that with a couple of fat blokes in the plane it is better to add an extra few knots before rotation (check your Pilot Operating Handbook for the exact figures) and then be careful not to climb out of ground effect too quickly !