Lindsay Lohan -- Jail Scares The Crap Out of Me ... So I Picked Rehab

It's not a promising sign ... but we've learned Lindsay Lohan did NOT accept the plea deal of 90 days in lockdown rehab because she wants to beat substance abuse -- she chose it because it beats jail.

We broke the story ... prosecutors have offered Lindsay the 90-day lockdown rehab deal for weeks, but she consistently rejected it. Her change of heart came at the last minute -- 30,000 feet in the air as she belatedly flew to L.A. for her trial.

Lindsay is telling friends she actually likes the rehab option, because it will allow her to focus on herself without any distractions.

Here's the problem. Lindsay is still saying -- ADAMANTLY -- she does NOT have a substance abuse problem. People in the rehab world say ... it's virtually impossible for anyone in rehab to get better if they don't admit having a problem.