I'm in my 9th year of living with PD. I used to freeze and fall a couple times a week, but reprogramming my brain has pretty much stopped that from happening any more. Not sure what caused the freezing in the first place (meds, pd, etc.), but panic always preceded a fall. As soon as my leg muscles froze, I would panic and not knowing what to do next, I usually fell. Fighting or resisting the fall only made it worse.
Once I realized what was happening, every time (well most of time time) I felt like I was going to freeze and loose control and fall, I would stop the fighting, stay calm and would carefully drop down to my knees in a controlled fashion. Better a controlled fall than an uncontrolled one.
Not to panic was the key. I next started to teach myself how to get that first step started again. I was becoming fully aware of what's involved in walking again. At first I would just focus on moving one foot at a time and slowly count out my steps. I would look at where I wanted to go (across the room for example: 5 steps) and count out the 5 steps. It's weird how this works, but once I told my brain it has a function to perform, it would automatically go through the motions. Becoming aware of my centre of balance helped me a lot too. I would consciously shift my weight to the stationary foot before I moved the other one. Concentrating on swinging my arms also helped in shifting my weight. I even started to swing my arms before my first step.
Look at where you want to go, eliminate any other toughs in your mind, don't try to have a conversation with anyone and become fully aware of your movements. It's not as easy as it sounds, walking involves dozens of muscles. Focus on one muscle group at a time helps. Walking again was the most difficult for me to do, I'm still reprogramming my brain, but I haven't had an uncontrolled fall for months now and only rarely do I have a controlled fall. The key is not to panic, stay calm and become fully aware of your movements.
Reprogramming the brain: Become consciously aware of your movements and don't take any movement for granted. I believe we need to relearn how to move again. This involves all muscles. Our bodies are constantly replacing old damaged cell with new ones. So lets program them. We can make new connections between the brain and the muscles. Reprogramming works best for me when I'm unmedicated and having difficulty moving around. I even had to reprogram my breathing. I would often find myself barely breathing, so I would consciously take deeper breaths. Becoming aware of my chest muscles going in and out. After awhile my breathing greatly improved.
Reprogramming the brain can start with just one finger. Focus on opening and closing that finger, then alternate with a finger from the other hand. As one finger close the other finger will open. This comes natural and without any effort when my meds are on, but requires mental effort when I'm unmedicated. The more I do it the easier it gets, try it. I believe I'm creating new neurological connections. Next try alternating one arm up and one arm down at the same time. By doing both sides at the same time, I believe it helps restore coordination.

It couldn't hurt...
Works for me.

Max