What could be the reason for the sudden loss of walking sensation in my legs?

Hello doctor,

I am 15 years old. My legs give out at random times while walking. It happens when I am simply walking, and I feel as if I forget how to walk randomly (this is extremely hard to explain). This has been happening to me for quite a while; sometimes, it happens more often than others. It is quite embittering, especially when it happens at school, and I am trying to get to class, and I randomly stop walking in the middle of the busy hallway, trying to catch myself from falling. I have tried walking in front of my mom before, but she thinks I am being dramatic. I do not exercise much and have never had any medical problems. I was in a recent accident and hurt my leg, getting a huge bruise, and months later, it still hurts, but I have had this feeling way before. I have tried researching, but the only thing I find is older people complaining about fatigue while walking, and as you see, I am pretty young. If anyone knows what this might be or if you have experienced this as well, please comment below. Am I at an average weight for my height?

Thank you.