I don't think YABU. My first did not sleep, day or night for more than an hour, if that and was bf for over 2 years. DP worked away so I was often alone for long stretches.
I went back to work full time after mat leave because I couldn't afford not to, sometimes working till 11pm having been up all night with no sleep at all.
But over time the sleep deprivation really ate away at me.
I developed such severe anxiety that I would be constantly thinking bad things were just about to happen. On my days off I wouldn't leave the house for fear of dying, sounds crazy, because it was.
I was so determined not to be late or have a sick day and I would leave 2 hours before I got to work, for a 30 minute commute, just incase I had to get off the bus to have a panic attack and sort myself out, which happened often and became a pattern.
No one at work knew this but they knew I was tired and my performance was awful.
Finally my manager recognised what was going on, his wife was off long term with anxiety and he couldn't believe I had managed to live like this for so long and encouraged me to get help ( I had previously been told that all women don't sleep by a male dr and that was that and I didn't seek further help then).
I remember taking beta blockers for the first time and it was like someone had turned the volume of the world down, only then did it hit me how bad things had been for so long.
They worked for a while then one day I left for work and had a major breakdown in the street. I was signed off for 2 months and suicidal and I'm lucky to be here today.
I think you never know if its going to be you who has MH problems, I never expected things to turn as they did.
I am glad your boss is sympathetic OP, I hope your colleague also gets the help he needs.
A Dr later commented that there is a reason that sleep deprivation is a form of torture.