I had a fall on 6/1/2012 that resulted in a non-displaced Lateral Tibial Plateau Fracture of my left knee.

MRI results:
IMPRESSION:   
1. There is a nondisplaced fracture of the posterior most corner of
the lateral tibial plateau. There is no obvious displacement or
articular surface depression, though the fracture does extend to the
articular surface. There is no obvious cartilage abnormality
overlying this fracture.
2. There is a 2nd area of bone edema of the posterior most aspect of
the lateral femoral condyle. This could represent an additional bone
contusion.
3. This bone contusion possibly indicates that edema overlying the
medial collateral ligament complex could indicate MCL strain injury.
There is also a significant amount of edema posterolateral to the
knee, though the major posterolateral corner structures to include
the fibular collateral ligament and popliteus appear intact.
4. There is also some edema in the proximal ACL region, though the
ACL appears intact. Stability of the ACL and MCL should be confirmed
during clinical follow up.
5. There is no demonstrated evidence of a lateral meniscal tear. The
medial meniscus also appears intact.

My Doctor sent me to Physical Therapy on Tues 7/17/12. I was at -20 degrees when trying to straighten, and 90 degrees when bending. Things went fairly well, with some minimal pain. She gave me some take home exercises to do, which I did, as directed.

I went back on Thurs 7/19/2012. I was at -15and 100 degrees. While I was there, doing the "Knee and Hip Flexion -Heel Slide" (Where you lay with your good leg straight, and slide your bad leg back to your butt), My knee suddenly popped on the outside (left side) of my knee. It hurt pretty bad.

When I forced myself to do the exercises on Friday, I felt as though my knee was going to pop again, so I stopped that exercise for the day. On Saturday, I tried again, and just went slower, and didn't try to go as far back. All was going well until while I was holding it in that position for the 10 seconds as directed, and suddenly, without warning, it popped even harder on the inside side of my knee (near wear the break was) and my knee jerked all the way back towards my hip and got "stuck" there for a few seconds!

It hurt so bad that I thought I would cry! I went to the doc today to get an X-ray again to be sure that I didn't re-break it or something. He said all is fine and that I will have a difficult 6 weeks or so as I try to regain my ROM.

I knew there would be pain, and I was fully prepared for muscular pain and soreness/pain, but definitely not this! I am finding it hard to find the courage to keep doing that exercise, even though I know I have to. The biggest issue I am having now is the sheer terror of the anticipation of the next pop, which I can tell is imminent. It's very hard to do, knowing that sometime during the exercise, somebody is going to come hit you with a baseball bat, lol!

 My questions are:
1. Is this normal? Has anyone else experienced either the pain or the horrible anxiety?
2. If so, did it go on for an extended time or did it just happen a few times to break up scar tissue or something?

Thank you in advance for your help/advice.