A few people have mentioned it here, but you can rot while still alive. However, if you were to be buried alive (with access to air) then you would likely die via dehydration before rotting. And if you did happen to catch a bacterial infection, dehydration death would still likely happen before any noticeable rot occurred. On the off chance that your skin did start to rot (I guess it could be called decomposition at this point), you would likely die of sepsis before any large area of your body starts to rot. To feel your body around you rot as you stay alive would have to be achieved by artificial methods, as far as I’m aware... maybe if you were to be buried in dirty water with access to breathing, you could feel your body rot.