Sound like tiredness.
Do you sometimes get erections in the morning or while sleeping? or have they completely stopped as well?
A normal functioning male, even ones with, for example, psychological or physical stress related erectile problems will still get several erections during his sleep. You sometimes wake up with one, but in the good-old-days the only way to check for certain was to put a ring of easily rip-able paper (or "postage stamps") around your penis and check if they have torn the next morning.
If you DO get erections during your sleep then you know for certain it's not any sort of internal health issue, the weakening of a blood vessels, or cholesterol, or most commonly, a lowering of testostorone (one of the first things GPs tend to check)
Successful nocturnal penile tumescence (or 'Morning wood') but otherwise coupled with erectile dysfunction during the day is almost certainly in the areas of physical tiredness, physical stress, emotional or psychological stress.
Do you use an alarm to wake up every morning? including weekends?
Do you sometimes let yourself wake up naturally? You may have grown accustomed to being sleep deprived so gradually that you've stopped noticing but now your body is telling you it's no longer able to keep up.
How have you been emotionally/psychologically lately? Sometimes if you're used to always "being on the go" you can pass that threshold of stress without even noticing. You say to your self "I'm not stressed, this is just how I always am".
For some folks, their mood or temper might change. They might have a relative tell them "you've been in a bad mood lately", but some people they don't have mood changes, just physical changes and symptoms.
I once experienced a "Silent Migrane" at a time when I didn't even know I was stressed about something. It was very alarming, as I'm sure is suddenly not being able to get an erection.
Any way I hope some of those questions help you get to the bottom of it. I'm sure you'll be back to yourself in time