What would you recommend me in this case ?

When I have a big problem to solve, I typically tend to postpone all other things until I am done with that big problem. As an example, if my manager tells me to do something that requires high focus and attention for a long time, I drop other things such as answering emails, chat messages, or taking simple decisions. From his perspective, it makes me look like missing in action. I go one step further, if I have a hard task to finish, it even effects my private life; I stop going out or doing things until I am done with that hard task.

How should I handle this so that I can have a better life/work balance as well as get done both with difficult tasks and simple ones and I do not look missing in action?

Any answer is appreciated! :)