It is used colloquially in the way you suggest, usually in the context that you have been under pressure, stress, from work or for other reasons. You take a break and do something relaxing to unwind. The literal meaning refers to a spring in a clock, or string, rope, etc being wound or unwound from a bobbin, capstan, etc; when wound there is tension in the spring or rope, which is released when it is unwound.

It’s common in American English with that meaning. I’d say it suggests a tense starting point more strongly than ‘relax’, and the stress is often mental. I had a long day of physically hard work. I just want to relax tonight. I know things are stressful at work when she unwinds with a glass of wine Friday evening. It can also be used transitively: The cord is wound up. We need to unwind it before we continue. (Common) That’s a complicated story. Let’s unwind it. (Break it down, analyze it step by step. Less common)

Hello