When doing productive work, sometimes we loose all focus on ourselves, feel challenged and engaged, and time seems to disappear, is called:

Anxiety

Explanation:

When we are doing something that is worth for us and suddenly we lost. It happened mostly with all people on someday. We lost and we could not focused on ourselves and feel challenged because of competition. It create an anxiety in a person. It stressed out a person. This situation create mental health problem in a person. When we feel competitive and not focused on our health it leads to other mental disorder as well such as depression and stress. Thus a person should focus on their mental health. It is most important aspect of life. Take care of their health first and then work hard in healthy way.