On break

From Dwarf Fortress Wiki

Yes, dwarves do have days off; sooner or later, all dwarves will go on break for some time. There is nothing you can do to stop it happening, but at least it's less annoying than parties. A dwarf will still go on a break even if they hadn't been doing any work at the time.

How to stop breaks

They will take more breaks if they are thirsty or have no access to alcohol. Give them lots of booze to keep them active.

You can cancel dwarves' breaks by drafting them into the military and then immediately releasing them. This causes an unhappy thought if the dwarf has no military skills at novice or better. Some players consider this an exploit, while others think it is balanced by the unhappy thought. If all your dwarves have novice in even a single military skill, however, there will be no unhappy thought. You could rationalize this as having "military culture" at your fort if you wanted, but it's definitely an exploit.