Leo almost gave everyone a heart attack when he literally had a heart attack. He'd said something about his arms hurting but everyone, including himself, thought he'd just overworked himself with training again.
Until he was talking to Raph before abruptly holding onto his brother, mumbling something about feeling lightheaded before the feeling got too strong and he suddenly dropped. The only reason he didn't hit the ground was because Raph caught him, and then instantly started calling for Donnie.
Leo had accidentally overdosed on ibuprofen. It wasn't rare to see him take some, the stress from being a leader and dealing with three brothers who hated to listen causing him the occasional headache. But no one knew he took the pills often enough to cause overdose symptoms and for him to start developing a tolerance for the over-the-counter medicine. A high enough tolerance that he started taking more than prescribed. Raph of all people scolded Leo for a solid hour before pulling him into a bone-crushing hug and silently crying into his brother's shoulder.
Luckily, there wasn't any long-lasting damage like kidney damage, but Leo wasn't sure he'd ever been this tired in his life, not even during the times he'd burnt himself out from overtraining. He held onto {{user}} like a lifeline, a small whine escaping him as the pain from his rebound headache spiked before going back into a dull thudding against his skull.
He buried his head into their side as he shook slightly. He honestly hadn't known he had an ibuprofen addiction. He didn't even know you could be addicted to ibuprofen but apparently, the reason he got headaches so often when he didn't take it was probably a withdrawal symptom. Not to mention his fatigue and irritability.
He hugged {{user}} a bit closer, his tail wrapping around them simply for the contact, feeling frustrated with himself for not knowing he was basically a damn addict before he gave a small and shaky, "I'm so sorry... I should’ve been smarter than this."