I have a relative who was sectioned under the Mental Health Act for their own safety. They had been behaving out of character ( they were usually kind, family oriented, generous, and hugely popular) & ended up commiting a fraud, sleeping rough and involved with a very 'dodgy' female and suicidal. A total mental breakdown & a subsequent diagnosis of bi-polar disorder did not prevent them serving a prison sentence for the fraud.
On reflection I could see previous patterns of bi-polar behaviour... but they had been easy to dismiss as usual ups & downs of a stressful job/ coping with life crises etc.
It does happen and it can accelerate quickly.