I seems like the same thing happened to me this morning when starting my computer, so here is what I got:
Tried to run ps aux|grep caffeinate|grep -v grep but nothing happened
Typed in caffeinate -dsi and I could not input anything until I hit ctrl + c, so that worked
Then I tried caffeinate -dsi >/dev/null 2>&1 & and the result was:  574
Finally, I typed ps aux|grep caffeinate|grep -v grep and I got that result:Me 574 0.0 0.0 2455792 1248 s001 S 9:53AM 0:00.00 caffeinate -dsi
I hope it helps!
I will try one more time if if it ever happens again, to see if I get the same results.