Hi Miles,
Not to worry. I had two small HT's with Bosley (400 in 1995 and 488 in 2000) and had fairly extensive shock loss from my HT (for more density) on January 30, 2007. I can confirm NN wise words - it does come back!
The next while might be tough. When you have existing hair and are going for density, the "step back" for the first while can be a real jolt. Hang in, this will turn around.
If you want, take a look at my pics in the Album section. I will be posting my 4 month pics in the next couple of days, and things are on the upswing.
Keep the faith
Bayer