if they were caught in the rain and got chilled they may well have just stayed put. I had 2 on a sidalcea this morning and it rained at 6pm last night.
the fact that they are alive this am is a good thing.

They are solitary bees or ones that did not make it back to the hive and pulled over to the side of the road as it were to rest for the night. Once the morning sun and the rising temperatures get their flight muscles up to speed they will be off about their business again. The same it true for every daytime flying insect. Now you might ask, how is it that nocturnal insects fly if there is no daytime heat and sun. The muscles of the nighttime flying insects are different in that they do not collect heat but produce it by being antagonistic muscles in that the muscle fibers are arranged such that they rubb against each other producing heat by friction. This friction producing heat is made by very small quick wing movements. Have you ever seen a moth commence to quiver rapidly once it lands on something? Well, this is a heat producing movement made to maintain the flight muscles functioning temperature while they get nectar from the flower or a lighted window that they landed on. Great question! Oh, while I am on the subject of moths,....one thing leads to another on GOY:)....ever wonder why their bodies and wings are covered with hairs? The hairs baffle the reflecting echolocation clicks of bats making the moth harder to find; you might call it natures STEALTH technology.

As far as I'm concerned, yes it's quite normal for bees to spend the night in their favorite flowers. They do this with my sunflowers. They need the sun for energy and to navigate. Bees cannot fly at night.

Thanks everyone, it's fascinating stuff.