Three times stand out, each stressful in its own way:
DD's birth: She was 3 weeks late, so at 39 weeks they decided to induce. After 28 hours of pitocin-induced labor and 4 hours of pushing, DD was born. 24 hours later we were on our way home when my legs started to feel funny, weak, and almost numb. We got home and I took a long nap; 4 hours later I got up with a fever of 104.6, and in incredible pain. I couldn't walk or move my feet at all without being in excruciating pain. At the ER they said it was probably a UTI, gave me antibiotics and tylenol 3, and sent me home. That was on Friday... on Monday my fever was still 102 and I called my OB. I was readmitted to the hospital where I was diagnosed with a systemic infection and a separated pelvis. I was in the hospital for a week, bedridden, sick, in pain, with a baby who couldn't go to the nursery because she'd been discharged and wasn't actually a patient. DH did what he could but also had to work, and we were on the opposite side of the country from any family members. Very, VERY stressful 10 days!
Dec 2016, DH had bone surgery on his tibia. It all went really, really well for 3 weeks, and then it started to fester and rot. He was seen for infection on 12/31 and put on antibiotics, but they didn't help. On 1/13 he was admitted to the hospital for what ended up being a week, during which time he had 2 full debridements of the area just below the top of his tibia and a gastrocnemius flap reconstructive surgery, with skin grafting. He was then admitted to a nursing facility where he was off his feet for 6 weeks (to make sure the reconstruction/grafting took) and received IV antibiotics 14 hours a day. The surgeons were all pretty clear about how lucky he was; if there'd been about 2 cm more gangrene, he'd have lost his leg. If the flap and grafts hadn't taken, they would have had to amputate. Now he is home, still taking 4 antibiotics a day for the next 10 months, having regular PT, getting better every day, and making progress. It's been a long year, and it's going to be at least another year before he is back 100%, but his leg is attached, works, and he's alive. For awhile in January, none of this was guaranteed.
The WORST day was the day they thought DD had meningitis. She had all the symptoms: Fever of 104, stiff neck, couldn't tolerate light, splitting headache, her blood pressure would bottom out every time she tried to sit up or stand. I clearly remember holding her while they did the spinal tap, watching the fluid drip and knowing that my life could take a turn for the absolute worst at any second. She was in the hospital for 2 nights, on IV and bedridden. They never did figure out what it was that made her so sick, but that was the scariest time of my entire life.