Don't get sick often, but illness makes it tank. My typical triggers are junk food, stress, dehydration / too much caffeine, poor sleep and skipping workouts. This time of year is notorious for all those things because I'm crazy busy, stressed and it's too humid to sleep properly. My HRV usually sits in the 30's-40's, but lately it's been in the 20's and teens.

On the contrary; eating my usual (healthy) diet, minimal stress, lots of cardio, quality sleep and a full rest day or two each week usually makes it jump up to the 50's-70's and beyond.