It sounds like your management is pushing you to give more than it's reasonable for you to give. You need to really understand that it's more than is reasonable. (You yourself described it as "unreasonable deadline".)

And, based on that, you need to become comfortable saying "no" without feeling guilty.

I mean, in a crunch, sure. For a couple of weeks, sure. For six months? That's a management failure. It's not your fault, and you can't fix it. You may be able, by heroic effort, to temporarily prevent catastrophe, at great cost to yourself. But it's actually OK to not do so. It is not reasonable for you to pay the price for management's failures.