I broke my roommate's heirloom coffee mug, bought an exact duplicate on eBay, and now she thinks her hands are losing sensation

Back in March, I dropped my roommate's favorite ceramic mug on the kitchen tile. It shattered into fifty pieces. It wasn't just a regular mug. It was a vintage 1970s handmade pottery piece that her late grandmother gave her before she passed. She drank black coffee out of it every single morning without fail. i completely panicked. I swept up the ceramic shards, shoved them into an empty coffee container, and drove three blocks away to throw it in a public park dumpster so she wouldn't find it in our kitchen trash. Then I spent four hours reverse image searching the pottery maker mark from the base. I got lucky and found the exact same artisan model on eBay for $140. I paid an extra $50 for overnight priority shipping. The box arrived three hours before she got home from her weekend trip, and I quietly placed it back on the drying rack. She didn't notice the switch at first. But a week later, she was holding it at breakfast and frowned. She said the handle felt slightly lighter than she remembered and wondered if her hand arthritis was flaring up again. Last week, she actually booked an appointment with a neurologist because she is convinced she is LOSING sensory perception in her fingers. its making me feel like a monster. If I tell the truth now, I look like a psychotic liar who hid it for months. Why did I do this?