BTW, a highly disturbed sleep like he is describing is a common sign of burnout/depression/anxiety disorder. Do not ignore it! There are drugs and therapy, it is worth it. It is double worth it if you have the money to stay unemployed or have other ways of getting some extended rest, at least 3 months. BTW, there is even some chemical signalling pathway explanation for that connection. Or maybe it is hypothesized? IDK, it's above my knowledge level. But the correlation surely is real and strong.