I've been playing badminton for quite a long time, about 34 years actually, and I've never had any issues before. But lately, I've noticed that when I wake up early in the morning, I experience some sort of pain on my left-hand side. Do you have any idea why this might be happening?

It is possible that you are experiencing muscle strain or inflammation in your left hand due to repetitive use during badminton. I recommend taking a nonsteroidal anti-inflammatory drug (NSAID) such as ibuprofen (e.g. Advil) at a dose of 400mg every 4-6 hours as needed for pain. Additionally, you can apply a topical analgesic cream like diclofenac (e.g. Voltaren) to the affected area. Make sure to rest your hand and avoid activities that worsen the pain. If the pain persists, consult a physiotherapist for further evaluation and management.