Is your dad able to walk during these weak spells? This sounds like it could be related to something Rick and I both experience periodic episodes of paralysis where we cannot walk. We start out feeling weak legs. We both have gone through various hypotheses and my neurologist thinks I am a nut. It is not run of the mill PD freezing and we suspect it may have something to do with levodopa and metabolism of insulin or potassium.

Not really a solution or answer but more a point of comparison.

Laura