Howard, You could have air in the lines, but doubtful if they have worked fine until now. Just keep in mind that I have read here that some brands of brake pads give you the same feeling.

I believe some pad material expands when hot. Then the material contracts once the car sits and cools. So the first time you step on the brake on the next drive, the caliper pistons must move further to take up the space, causing a low pedal feel on the first application.
Just something to think about if nothing is found in the fluid system.

James