Would it be correct English to say "release stress", for example: "If you do not find a way to release stress, you will get tired, you may even fall ill."
Is "release stress" an acceptable collocation, or are there other ways to express the same idea in more idiomatic English?
It's perfectly fine, although relieving stress might be slightly more idiomatic. If you want a more vivid expression, you could consider letting off or releasing steam.
Compare relieve stress with release stress using Google Ngram:
This graph shows that both expressions gained popularity in the 20th century, though at different rates and starting points. Note that this graph does not discriminate between emotional and physical (e.g., mechanical) stress (thanks Edwin!).
The Oxford dictionary gives two definitions of "stress":-
1 Pressure or tension exerted on a material object:
2 A state of mental or emotional strain or tension resulting from adverse or demanding circumstances:
From the above it is apparent that the word "stress" was originally an engineering term which has come to be applied to an "emotional" condition.
In purely engineering terms, stress can be removed, reduced or relieved (by providing additional support). However, if engineering stress is "released", it could be because the cause of the stress has been removed (or taken over by another physical means of support) or the stressed object has collapsed.
Extending this by analogy to the emotional state, "releasing stress" would mean that the cause of the (emotional) stress has been removed or taken over by something or someone else or that the stressed person has decided to either "opt out" (let go) of the stressing situation - or to find another way to deal with the cause of the stress.
