How to regain lost focus? I seem to have lost the focus that I once used to have. Few years back I was able to study for 4 hours straight but now its hardly possible for me to focus for 15 minutes. Any advice on how to regain lost focus in studying?
This situation is not that uncommon and there are several approaches you might try. Few month ago I couldn't barely manage to sit down and start to read or write for my master thesis. Therefore, I also tried several of the possible approaches until one worked. The short answer is: Change something.


Plan to only study for 15 minutes straight, make a 5 minutes break and go back again to work for another 15 minutes and so on. If this works out, try to stretch the working time to 20 minutes and see how it goes. 
Turn on or off distractions, e.g. I usually need distraction and noise around me to study, so I gave the opossite a try. Turn background music on or off.
Change the place where you study. Relocate yourself into a coffee shop or a park. Look for a shared workspace and try coworking.
Play games or challange yourself by setting small achievable goals and honor yourself for achieving them with whatever you like, e.g. some time off or treats. I know that this one sounds kind of weird but give it a try.
Take a longer break for several days, if you can afford this in terms of time.
Turn the internet off, i.e. no smartphone, no browser.
Try other working hours like in the morning or in the night.
Mix the material you have to study or the methods you use, like watching videos, reading, writing, summarizing, structuring, collecting.
Add physical exercises to your routine, e.g. short exercises of only a few minutes every hour (stand up, stretch, walk) and/or more challenging exercises once a day or every few days.


I'm pretty sure that there are much more options. These are only the ones I personally tried. Good luck.