u/Miss_paris_22

either ...

1. Ladybug’s Miraculous is damaged during a fight and slowly starts killing Marinette. Every transformation makes the corruption spread further — hallucinations, memory loss, violent mood swings, terrifying paranoia — but she keeps using it anyway because Paris still needs Ladybug, even if Marinette is dying.

or

2)Marinette develops severe sleepwalking episodes due to stress and guilt from lying to Adrien, resulting in everyone believing she attempted suicide after she’s found standing on her balcony railing in her sleep.