Most stressful- Long term acute care. Least stressful- private duty pediatric nursing. Some kids with trachs/vents. Other times I've had only a baby that needed a cath every 3 hours or g-tube feeding! Most enjoyable (for me)- NICU. Never boring, but it wasn't too stressful- all of us nurses were in one big room so if your baby needs help you can get it quickly.
I've never approached "someone that looks sick", I feel that would be intrusive and I wouldn't want someone to do that to me. If someone asked me to I would. If they look like they need an ambulance I would approach and see what I could do to help. I've checked vitals in an emergency situation of course- there were two young adults hit by a car that drove off outside of my apartment and I heard it happen.