You're human - it'll happen. Be diligent. Try to work when you're supposed to be working. If you honestly can't work when you're supposed to be working, or if you can't get enough done because of personal issues, then either put in for a "personal day" or put in longer hours to make up for the time lost.

You are a person, and entitled to your feelings, and yout personal concerns. Equally, your employer is entitled to the time they pay you for. Be honest and diligent, but don't feel that you have to push on regardless and at all costs.

Strive for balance. If you need to take a little time, talk to your boss. Explain that you need a little personal time, but that you will remain on-call for anything urgent.

Or something.

If one of my employees came and said they had some personal issues they needed to deal with then I would work with them to find an appropriate balance between the work I have for them, the pay I give them, the time they give me, and the fact that I want them to stay healthy and productive. not just for me, but for us.

Not all bosses are like me. Some are worse, but some are better.

Above all, don't try to be a machine. Shit happens, and it can hurt. There are some things that never get better, but we do get better at dealing with them.

Good luck.