Should be fairly comfortable; but tiring. Good question actually. CC on such a long journey can be strenous. As for sleeping, well, you have to make your own arrangements (please don't take this as a serious answer), you can use the aisle with discomfort to other travellers.. I guess others in the CC will be doing the same. If the CC is not crowded, then you can use one method which I used to do in the former AC Expresses between Delhi-Calcutta and Delhi-Bombay - use the empty chairs next to you, wriggle as much as you can under the arm rest, and crouch and SLEEP. :) I have done this on Economy class in the international airlines.. Good luck and good wishes.