I seem to be doing that today - I also almost ran out of gas on the way to work. I meant to stop on the way home last night I forgot to, and then this morning I jumped in the car and got right on the highway to work. Fortunately I noticed the gas light on just before I passed the last exit on I290 that was still close to facilities. If I'd been further along I'm not sure I would've made it to a gas station.
I think it is just fatigue - not enough sleep and too much stress (hectic week), and my brain isn't keeping up. I just hope I'm not forgetting anything else, especially anything important.