One of our electrical breakers has started tripping - twice in two days but had never tripped before (12 years). Does this indicate we might have some problem?

Have you added any new appliances, heated blanket, room heater? You could have an overload, an occasional short or a weak breaker. I'd start with the breaker, most are <$10. Fairly easy to replace but if you have never done it before, I'd suggest an electrician.

Has Christmas Lights been added?

Great questions, can't give much advice until you answer the guys. If this breaker is identical to other breakers in the panel I would consider switching wires with a different same size circuit. If the problem moves to the new breaker you have an overload. If the problem stays with this breaker then replace it.

Just thought of something else. Is this a GF breaker? If connected to an outside circuit and XMAs lights are getting wet, it will trip.

Merry Christmas!

Before you start changing wires on breakers or even changing breakers, do you know what to touch and what to stay away from in either a live or dead panelboard?

If you do not, then stay out of the panelboard cabinet and please provide us with a complete description of the entire circuit and what devices are attached.