Use 'sciatica' primarily in medical or health-related discussions to describe specific lower back pain. After the car accident, the doctor informed him that his consistent pain was due to sciatica.
Pro Tip 2/3
Not Contagious
'Sciatica' refers to a condition, not a disease, so it's not something you can catch from others. Although my sister has sciatica, it's her individual struggle and cannot spread to me.
Pro Tip 3/3
Serious Pain
'Sciatica' implies severe pain which may limit someone's mobility, not just mild discomfort. Her sciatica is so severe that she can hardly walk to the kitchen without wincing.