baseballmom2,
It is known that sitting places more stress and pressure on the spine, than does lying or standing. You may be stressing your fusion mass, and the remaining discs.
You could try taking more breaks where you get up and walk around, rather than sitting for extended periods. That is one problem with modern offices, with the computer. Physical activity is factored out.
We no longer have to reach down into the lower drawer to get out a piece of paper and then reach up and put it in the typewriter. We don't have to reach up and move the carriage back at the end of each sentence. Oops, made a mistake. Get into the desk drawer and get out the white out, reach up, lean in, correct the mistake, move the carriage back to the current sentence. Okay, document finally done. Reach up and take it out of the machine, find a pen, and sign it. Get an envelope out of the other lower desk drawer, and address it. Now, get up and walk over the the filing cabinet. File the carbon copy. Walk to the mail room, to mail the letter you just wrote. Walk back to your office/desk, and start on the next document. On the way back to your desk, pick up some supplies or the mail. Basically, we used to move around a lot more than we do now.
Now days, all we do is move our fingers, and hit "send" to have the document sent all over the world.
So, it is a good idea, that at the end of every document you do, get up and move around. Do a little stretching, walk around your office for a few seconds. Then start on the next file/document. We need to get the bending, moving, stretching, walking, back into the office environment.
You are going to have the ups and downs during rehab. Remember, it takes about a year to fully recover from a surgery like this. You are doing fine, it sounds, and just had a bad day. It's going to happen.
If you are really concerned, contact your surgeon or make an appointment to see him/her. Hang in there.
Good luck.