Perhaps Tabs? Teeny weeny tabs, tabs everywhere? 
That seems unlikely.
Verify that the laser PWM is still set to 20 kHz: Edit → Machine Settings → Vendor Settings → Laser Settings → Laser 1 Frequency. There is no way that should change, particularly just occasionally, but it’s easy to rule out.
Similarly, the layer settings have a PWM override, but it would take a concatenation of unlikely finger fumbles to both activate and change it; you would have noticed when you verified that Dot Mode was turned off.
Absent all that, you’re probably looking at a failing power supply or (shudder) a failing tube. The fact that the beam cuts differently along the X and Y axes suggests the beam is no longer circular; it might be longer in the Y direction and blurs the dots together.
Compared to tubes, power supplies are (relatively) cheap and readily available, so swapping in a known-good replacement would be a quick-n-easy check that it’s not sending Morse code to the tube. A bad supply would not cause the X vs. Y variation, however.
Check the tube’s lasing mode. Put a paper target at the first mirror and fire a 50% pulse that’s short enough to scorch but not punch through; you should see a nice round spot with a darker center.
Recent pix and discussion of lasing mode (and other stuff):
This may be one of those simple problems with a spendy solution …