A short sci story from a paperback anthology I read in the early '70s, plot stayed in my mind ever since but can't recall author or title! People mysteriously start to commit suicide in electricity stations, eventually becoming a nationwide epidemic. Starts with scientist / detective being called to investigate initial case/s then escalates into darker dystopian societal breakdown. Was gripped by it as a lad.
I have a partial match for you: All the Myriad Ways by Larry Niven.
It's the right date, 1968, it is about an epidemic of suicide, it does involve a detective looking into the problem, and it does end gloomily. This all matches. However the suicides are not by people breaking into electricity stations, so it could only be the correct story if you've conflated this element with some other story.
The detective is Gene Trimble. He is investigating a series of suicides (and murders) that started after a technology called Crosstime was invented to explore alternate timelines. It happens because people realise that no matter how fortunate they are there is always a version of them in an alternate timeline who is richer, more successful, healthier, etc, etc and they find this knowledge impossible to live with.
The story ends:
Gene Trimble looked at the clean and loaded gun on his desk. Well, why not? ...
And he ran out of the office shouting, “Bentley, listen, I’ve got the answer ...”
And he stood up slowly and left the office shaking his head. This was the answer, and it wasn’t any good. The suicides, murders, casual crimes would continue. ...
And he suddenly laughed and stood up. Ridiculous! Nobody dies for a philosophical point! ...
And he reached for the intercom and told the man who answered to bring him a sandwich and some coffee. ...
And picked the gun off the newspapers, looked at it for a long moment, then dropped it in the drawer. His hands began to shake. On a world line very close to this one ...
And he picked the gun off the newspapers, put it to his head
fired. The hammer fell on an empty chamber.
fired. The gun jerked up and blasted a hole in the ceiling.
The bullet tore a furrow in his scalp.
took off the top of his head.