Been on Clonzepam / Klonopin for a year, I take 2-3mg a day.

.5 is a small dose, I believe seizure sufferers take upwards of 8-12mg.

Anyhow, 2mg doesnt make me sleepy, doesnt hit me and do anything direct, and as stated has a long life span and stays in your blood 24+ hours. If you take an extra one, although obviously not directed. (it can become an addictive med) It wont do much to you except possibly add some dizzyness and tiredness. I find going from 2-3mg on "bad" anxiety days tends to make driving more hazardus (I tend to nod off) other then that I dont notice anything else negative.

I have a friend who will down 6-8 mg when he feels like an attack is coming. I always warn him not to, and that its stupid to jump your dosage like that but he does it anyway. But nothing happens to him, other then being a little out of it. So anyhow my entire point is taking and extra .5 although not reccomended since you just have your doc tell you to take the extra, probley wont do anything bad to you.