There is a terrible pressure to stay in high gear at all times in today's culture. There's a hidden message that with enough caffeine you should be able to go go go all day and night.
Of course you can't run your metaphorical engine in the red nonstop any more than you can any real motor. You've got a certain capacity, which you most definitely should exercise the fullest quite often, but slow down and recover afterwards.
There are things we fundamentally need to stay happy and healthy and wise.
When that little voice in your head is saying "Too much!", be sure to build a rest into your schedule as soon as possible. If there's a crisis, you might need to make it a shorter rest, but there is always a way to take a few moments to step out of the noise, look out to the distance, breathe and rest your mind.
When that moment comes that you can't take the longer break you need, at least schedule it. Plan to use a vacation day, give your regrets for that social obligation that was going to take up all of Saturday, skip the TV tonight and go to bed early.
It's really truly definitely okay that you can't Do It All all the time.