I had a sudden auto immune reaction about 6 years ago that left me in severe pain and barely unable to walk with severe swelling in my knees and feet. Feet were constantly covered in blisters. i had to take time off for specialist appointments and eventually i also developed a cyst on my back that went misdiagnosed for a year before i got surgery so understandably i wasn't doing well mentally and i was suicidal. I unfortunately also brought my bad mood to work and really struggled to keep up. I'd also just moved out of home on my first salary job so i wasn't earning much to pay for medical expenses.

However during this time i had a co worker who:
-Started up an email chain with another employee in our department trying to come up with ways to get me fired.
-Went to my manager telling them i don't deserve a promotion despite me saying i didn't want it (i actually recommended them for it) and then they still went to the next level up telling them how awful i was and that i they shouldn't promote me.
-Would harass me on social media while i was at doctors appointments because me talking to people online while i was traveling or in a waiting room somehow indicated to them that i was lying about my condition or appointments
-Sent me emails telling me i was doing a shit job
-not once thought to say "hey are you doing ok"

Thankfully that shit was sorted out by management eventually but yeah, Bullying someone who clearly wasn't doing well because they made your job slightly more difficult was the cool thing to do and i really struggled to get over that whole period in my life. I blamed myself for all of that but in the past year or two ive kind of realized that it was such a shitty way to treat someone.