I've had this happen before. For a six-month period I was able to finish my day's work and then head home and spend another 3-4 hours focusing on my own stuff.

I've had this happen before. For a six-month period I was able to finish my day's work and then head home and spend another 3-4 hours focusing on my own stuff. After having a three-week vacation, I lost this ability. I couldn't focus anymore. I was back to being a regular person. Things I did to get my focus back: One is that I introduced sugar/caffeine back into my diet. Drinking a sugary, caffeinated beverage improves my ability to concentrate significantly. While this might not be right for you, you might find that some of your other dietary choices are affecting the supply of glucose to your brain. Another is routine. If you had the ability before, you can get it back again. One thing that helped me return to my groove was listening to the same music I used to listen to while concentrating. Having an album in the background on repeat can work wonders. Maybe there are some other important concentration triggers that you need to tap into. Lastly, maybe your work just isn't that interesting. Rediscover what things you actually want to be working on. Get excited about something again.