What everyone has said is correct. In Chinese, they don't usually straight up say "I have [an] anxiety [disorder]." I don't really know why...I think things like mental health are bigger taboos in East Asia. That or maybe naming all of our mental health issues is more OK in Western Culture ("I have anxiety," or "I have depression" don't quite translate the same way in Chinese).

忐忑不安，焦急，焦虑不安，担忧

一直都很紧张 as you have said. Any problem?

There're also these ways of expressing in modern Chinese. They are common. :) You can just say "我有...." or "我患有...." I have anxiety. 我有焦虑症 I have mysophobia. 我有洁癖 I have melancholia. 我有忧郁症 I have ADHD. 我有多动症 I have depression. 我有抑郁症

Just like you said 我一直很紧张 or 我一直很焦虑。The key word : 一直 means always , 紧张means nervous, 焦虑 means anxious.