If you have issues with insomnia, you should get that looked at first. I think your QoL will improve dramatically if you fix that first.

What makes it easier to ride in? Well, my commute by bike only takes about 10 minutes longer each way than if I drive; that helps.

Regarding feeling sick, I find that a bit of exercise makes me feel much better. Helps relieve congestion due to allergies and colds. And, for healthy people, even strenuous exercise has no effect on the duration of a cold.

But the main thing that makes it easy, is that the thought that tomorrow, it won't be so easy. What if it rains tomorrow? Not as fun a commute on the road bike. What if I find out I need my car at work, to drive to a meeting? There goes a day. What if I get fat, get old, and can't bike to work anymore? That's what'll happen if I put it off for too long.