First guess would be yes, to much mojo going on at to slow a speed. Thats really loading things doing that with a servo system, you add the heavy weight of the head and it gets worse.
Of course there is always the chance of it just being a freak thing that the drive blow. ALso I would keep a eye on that servo because if it has a internal short thats trying to start acting up you might have problems again.
One thing I have always thought everyone should do is run temp reading equipment on the drives so you can see if things are getting in a strain. The drive will get hot if so. ALso some are using amp meters to help watch things.
All you can do is chaulk it up to gone for now and keep a eye on things. Be sure you use good thermal paste on the back side of the drive and good air flow/cooling for them. At 48v you would think you would not be pushing the drives that hard but its the amps that can get you the most and on a Bridgeport that can load things pretty quick. I plan to put temp reading equipment on each of my drives and maybe even amp meters. I am a little shy on the amp meters because of some info I was reading that was trying to claim it being a bad thing to put them in line but I feel like one with a good heavy shunt would be no problem. It would be pretty easy to build a little system that keep a eye on the temp with a PIC and some thermisters. It could even be setup to give warning signal or possibly even cause a fault or E-Stop if done right.
Make sure the wiring didn't take a hit and now has a lot of resistance built up in it. This could be worse than a bad motor. Connectors and power supply itself should be looked at close. Hopefully it was just a freak or a overload. The overload is something you see people do every now and then so I would guess that being the case. The servos like to run in the RPM not at low load. In fact any quick load that stops a servo is a bad thing and should be avoided.