Tapering 0.5mg clonazepam took for 19 months once daily. feel anxious,irritated,depressed. day 6 of taper. when will it subside?tapered to 0.25mg.

Likely not physical: dependency at that low dose. I have had patients who appeared inordinately sensitive and needed long-term taper from low doses, but they were few and far between. If you are going to taper from that low dose, a VERY VERY slow taper is indicated, probably reducing the dose by 0.125 mg (1/4 tablet) every two-four weeks would be my recommendation. It may well be return of underlying conditions.