21 Bizarre Side Effects of Becoming a Running Junkie

15. The Disappearing Toenails Phenomenon

It's a badge of honour (or horror) for many distance runners. Repeated micro-trauma from your toes hitting the front of your shoe, especially on downhills or with ill-fitting footwear, can cause blood blisters under the nail, eventually leading to the nail detaching. While typically painless as it occurs gradually, the sight of a "black toenail" or a missing one becomes an all-too-familiar part of your routine.

16. The "Is That My Heartbeat?" Auditory Hallucination

When lying still in bed or during quiet moments, you might distinctly hear your own heartbeat, a deep, rhythmic thrumming in your ears. This isn't necessarily a medical issue, but rather your cardiovascular system becoming incredibly efficient and your body becoming acutely aware of its own internal workings. Your resting heart rate drops significantly, making each powerful beat more noticeable.