Monday morning, international office. Your Japanese colleague, beaming: "The party on Saturday was so high tension!"
Your brain: someone got punched.
Her brain: everyone was singing.
Both of you smile and move on, and a small misunderstanding takes a seat in the corner and stays for the whole quarter.
テンション in Japanese does not mean strain. It means mood level, energy, buzz. テンション高い = hyped. テンション低い = flat, not feeling it. テンション上がる = "my energy is going up", i.e. I'm getting excited.
This is one of the highest-frequency Japanglish traps in a workplace, because it produces sentences that are grammatical, confident and completely inverted. "He was high tension in the meeting" means he was enthusiastic. Not that he was moments from resigning.
It also gives you a phrase English genuinely lacks: テンション上がる is not "excited" — it is the physical sensation of your energy rising because of something specific. New shoes cause it. A song causes it. English has to build a whole clause for that.
Japanese borrowed a word about physical force and reassigned it to emotional voltage — and then built a full set of controls on top: high, low, rising, dropping, someone "killing" the tension. English has nothing this tidy for the thing we all obviously experience. We just say "vibes" and hope for the best.