The plan I prescribe is just taking more mental breaks. Resting is difficult, but you obviously need more of it.
Your mind is just as active when it isn't focusing compared to it being hard at work. When you rest, your mind sorts out the things in your head. This happens most effectively when you sleep, but it also works in smaller amounts any time you zone out, daydream, drift into the subconscious.
When you don't get enough rest, your mind starts to do that processing wherever it can. This is what causes you to lack attention. A big part of it is bad habits too, often things like checking email or notifications every 5 minutes.
1. Quit social media, games, and forums (including HN). Social media is a tremendous drain on brain power. You can come back later, but I would recommend avoiding it until you have recovered. Basically, social media forces your brain to keep running, giving it new things to process, when what you want is some dead time.
2. Schedule the time when you have to do stuff. I recommend a block of work, minimum 30 minutes, max 2 hours. Schedule breaks too.
3. Get more rest. If you're feeling burnt out and not excited, you have too much stress, too little rest. You know that you have too much rest only when you are getting bored.
4. Resting means doing nothing. No TV, no games, no internet. It's all you and your subconscious. This can be meditation, walks, shower, spa, swim (or float), watching a movie with friends, sitting at a nice cafe or library.
This is very hard and will make you feel anxious, especially if you are used to a hard pace. Anxious is normal.
I split my days into two types: either "lots of pain" or "recovery".
If you find yourself just wondering where the day went, you should either be pushing yourself harder, or taking a break.
For more details, check out the books Peak Performance and Deep Work.