That works the same with alcohol - heavy alcoholic would probably need to be over the limit to feel ok and sober.

An important point is that drug users (alcohol included) lose their ability to judge their own impairment after a lot of habitual use.

They can even develop an ability to appear sober to casual observers while being impaired.

Feeling sober is not a reliable indicator of being sober. It’s referred to as delusions of sobriety.