Yep. Walking down the stairs is the killer. It seems counter-intuitive. People think walking up the stairs will get you. Nope, more people going down the stairs get injured.
I was using a walker coming out of the hospital after months in bed. At home, I have 16 steps up to the 2nd floor where the bedroom is located. I have 16 steps down to the basement where my home office is located. Initially, I could only hold the handrail and put a foot up or down, then follow up with the other foot. It took 10 minutes to get upstairs when I first arrived home. Down was just as bad. I didn't even attempt the basement. Over time, I rebuilt enough strength to climb or descend with a normal left/right gait. I can go basement to main floor to 2nd floor in about 30 seconds now. Adding 3 grams of HMB to my daily diet has helped rebuild the necessary muscle.