We live in a cult of busy. Busy has become a humble brag instead of an indicator of stress. Researchers say that we talk about being busy so much because busyness conveys social status. Busy people are important people. If you aren’t busy, you are obsolete. And when a colleague asks you how you've been, instead of defaulting to “I’m busy” for an easy answer, talk about your recent wins and projects that you’re working on. Everyone’s busy – we’d rather hear about how you’re managing your priorities – not how your priorities are managing you. Here's what you should aim to say instead of "I'm busy":
'I'm very productive today'
Such response will save you if you're afraid that your boss will assume that you're doing nothing if you're not complaining about heavy workload. You still sound busy, but at the same time you're happy about it. Take a moment to celebrate your work and your contributions. Besides, such positive attitude is contagious. Your colleagues will appreciate a moment of good mood. Saying something like 'I'm busy/tired/stressed out' is nothing but complaining. It not only makes you sound less motivated, less willing to jump in and help, but it also makes you feel that way too.