Call off the search party ... Kate Major has been found -- and it turns out ... she was never really missing in the first place.
As TMZ first reported ... Major was taken from rehab to a nearby hospital in Florida Saturday night, after suffering a seizure -- but when the rehab facility called to check on her hours later ... the hospital had no record of her.
Kate's rep and family were completely freaked -- but it was a false alarm ... because Major was in the hospital after all ... just under a false name for privacy reasons.
Major's rep tells us ... word got back to Kate that she was considered MIA, so she called her father and told him everything was fine. Mystery solved.