That is absolutely possible. I remember getting burnt out many times in my twenties. I think one thing that helps is to remember that burn-out is a temporary phenomenon. If it lasts for longer than a month (and I've experience this), then you need to proactively take steps to try and fight it.

I recently overcame a severe bout of burn-out using the Pomodoro Technique and an Android app on my phone to manage it:

https://en.wikipedia.org/wiki/Pomodoro_Technique

What this did is help compartmentalize my time. If you can focus on your work when it's work time, then you can relax and free your mind when its free-play time. Remember, you don't need to be productive for eight hours straight, just a 25 minute sprint. Then take a break and try another 25 minutes when you are ready to focus again. Pretty soon you'll be getting a respectable 4 hours of productivity in a day and that's more than most people can claim.

Most importantly: keep fighting the burn-out. If you keep facing it as a problem and keep actively trying to find solutions to it, you will get better and more efficient and beating it back when it does arise. I'm really sorry you're experiencing it at the moment, but I sincerely hope you get past it quickly and grow adept at recognizing when it's starting to happen again. You are not alone or even unusual in experiencing this.

Even at 40 hours or less people can become exhausted. What matters are abstractions like traction, relevance, independence, and opportunities to demonstrate skills. Being stuck or having a hard time contributing can tear almost anyone down rather quickly.