I don't believe it's claudication, though I'm not a doctor, and this is a new one for me.

What leaves me believing this is something else is this doesn't happen when I'm out walking at all. I also began recently experiencing spasticity in my left leg (same leg as the buckling is happening to) but ONLY 1. during the night (wakes me from sleep often, interrupts sleep) 2. when I stand up too quickly and try to move quick, especially on very humid days.

I noticed something else last night about the buckling... this is happening primarily when I am doing something that involves 1. standing in 1 spot 2. leaning forward/bending

Was brushing my teeth before bed last night and leaning forward to look in the mirror, bent a little, and wouldn't you know it? Buckled leg. Caught me off guard but luckily I was leaning on the counter.