Lil Wayne said ICU later to Cedars-Sinai Medical Center in West  Hollywood ... because TMZ has learned he was just released.

Wayne spent 6  days in the hospital -- most of it in the Intensive Care Unit -- after suffering  what appears to be a drug OD that triggered a series of massive  seizures.

Sources connected with the rapper tell us ... Wayne is feeling  weak but he's a lot better.  He plans on laying low until he makes a full  recovery.