Why can't I turn off the alertness my job requires?

You have started to see it clearly: the alertness your job demands did not stay at your job. It became the way you move through everything, always scanning, always braced, even when nothing is wrong. Seeing this is the important first step. Most people never notice the shift; they just wonder why they can't rest. What kept you safe or sharp at work becomes a burden everywhere else, because the mind does not have an off switch you can flip at the door. The vigilance is a habit your body learned for good reasons. It is not broken. It just needs to be taught that home is not the job. Start teaching it with one small signal each day. When you get home, do one deliberate thing that means off duty now: change your clothes, step outside, take a few slow breaths. Do it every time. You are not forcing yourself to relax. You are giving your body a border it can learn to trust.