+1
I'd suggest that it should be a single out-and-back motion, like a concussion rather than an actual reciprocating "shake" motion. It might also have a very quick redout and/or blackout (this wouldn't be optional) which would reflect the amount of explosive energy that hit you (roughly explosive weight/distance^3)
An a semi-related note - I do recommend a subwoofer. I have 8.1 Surround sound by Creative - it isn't fancy and I got it free, but when I crank it up, the engine noise shakes the house, and the explosions rock. I have the comms channel through my big earcup headphones, and I need the headphones to cut down the external noise. Surprisingly realistic.
Cheers!
Paul