Stalling while idling?

Hello, I am disabled only driving around town. Have the oil changed every three months. It is taken care of by a mechanic I've had for years. Recently it stalled while waiting at traffic lights. No service engine light comes on. All electric still works. I usually wait a while then it restarts. This has happened four times now. The first two times were a few weeks apart. Today it happened twice within a couple of hours when out doing errands, so tomorrow it goes (back) to the mechanic. When it first happened, he kept my car for a few days. He drove it, took it home, no issues. When I spoke to him today, I told him it's no longer safe for me to drive. He agreed. He mentioned possibly changing the main relay. Today a police officer seeing my DP plates and emergency lights, stopped and restarted it for me by turning the key to accessory and back about five times. Any feedback is appreciated.