What did your boss say in the message? I know it's easy to jump to worst-case scenario, but might just be checking to see if you're OK. Or even if it is about the lateness/absences, could just be a discussion about it rather than a firing.

That's good you see your p-doc Friday. Maybe you need a different antidepressant, too? Or something to augment what you're on (I forget what you're taking), like Wellbutrin or Abilify (my p-doc was discussing maybe adding Abilify to the Zoloft I'm on).