Bike shimmy / high speed wobble.

wind700
wind700 Posts: 17
Has anyone experienced speed wobble when descending ?
Two weeks ago i crashed at 38 mph on a descent from Coldharbour to Dorking in the Surrey hills. The handle bars started to oscillate violently left and right and I couldn't control the steering. I ended up in the edge of the road in the gravel and dirt at edge of the country lane.
I not sure what caused the wobble but I had my bike serviced the previous day by a very reputable bike shop. I had the wheels that are fairly new trued but I think that maybe one of the wheels my be out of balance. How do you check wheel balance and do bike work shops actually check wheel balance.
I suffered 4 broken ribs a punctured lung and a broken collar bone.