Sometimes, you need a day. When you have a job in tech, the amount of available knowledge to us can both incredible and staggering. We fear to look unintelligent to our peers and colleagues, so feel obligated to learn everything we can. The desire to learn is not the issue here, though. What's important to remember, is that it's impossible to learn everything.
You can spend hours on end reading up on the newest frameworks and testing them out, but you know what? That framework will still be there tomorrow. You don't have to spend every waking or free hour writing code. I'm not saying you should procrastinate learning or give in to Resistance. All I'm saying is, really listen to your body. If you're falling asleep while sitting at your desk or on the couch, it's probably time to take a nap or go to bed. If it's taking you 3 or 4 times as long to complete a task because you're feeling anxious, it's probably time to step away.
Don't be afraid to put some things down for a minute. Your best work is done when you're feeling your best. But if you can't put the things down right now, make sure you are taking breaks. Please don't put your own health on the line for this. One day will not put you behind. Care for yourself. You deserve it.