Your 240 volt electrical service has two hot conductors. One of them is likely failing.
I have seen weird things happen when only one hot feed is missing from 240 volt service. 120 volt devices plugged into the 'dead' side of the panel can provide an in-series path to neutral for 240-volt devices, thereby allowing in-series 120-volt devices to operate at reduced capacity that can vary depending on how many other 120-volt devices are also turned-on and which 240-volt appliances are also in operation at that time.
To determine if there was possibly any initial change with the situation, I asked Cheladamama to report her findings after resetting each 240-volt 2-pole breaker including the panel's main breaker. Unfortunately, she did not do so.
Sometimes one 240-volt breaker may trip but may not have sufficient force to also trip the joined non-overloaded breaker. Often a tripped breaker may not necessarily appear so in not having moved fully to the tripped position. By requesting she shut-off and reset each 240-volt breaker, was an attempt to ensure a tripped 240-volt breaker was not the cause of her issues. If resetting each breaker did not resolve the issue, then verifying the incoming power using a volt meter inside the panel will likely have been the next recommendation.