Answer: Well , a lot of things can cause a sudden change in someones life and personality well here's a few i can mention
physical illness can cause personality changes.
Stroke, brain infection, infection or injury can be serious problems. Dementia, Alzheimer's and even body issues like digestive disease or heart disease can all cause personality changes and require immediate attention.
even a broken heart can cause a change in someone's life.
Step-by-step explanation:
Fact : A single negative thought can change your mood or spoil your day.
Well i hope this helps .For more info , contact me in the comment section :)