A personal upset or problem can often make pressures at work feel more unmanageable than they really are. So:
BEFORE LEAVING HOME note down what you intend to do about your problem on your return. Leave the note at home.
TAKE TIME OUT TO EXERCISE as this releases tension. Or distract yourself with a good book on the way to work.
SHARE YOUR PROBLEM with one good listener. Say you just need to let off steam so you can focus better on work.
DEFEND YOUR PRIVACY. Tell the 'do-gooders' you appreciate their concern but would rather not talk about it at work.