Hey Mike C. I am taking 0.5 mg Clonazepam as needed too. When I first took one, I only took half because I was worried about taking meds. But even taking only half, my body felt similar to what you described you felt. I am not positive or anything, but I believe your body is just responding and adjusting to something new. It felt really weird to me and so I was worried to take another afterwards.
A few days later, I took a full 0.5 mg dose in the evening, and once it kicked in, I felt fine really. I didn't feel any of those weird sensations that I had the first time with only half dosage.
Everyone is different, but maybe the next time you take one, you won't feel those weird sensations you had the first time?