Toenail loss. Why is it coming off? Usually prior injury can make it come off but the injury could have been many months ago, six to even 12 months before the toenail comes off. Pain is rare. See a podiatrist or dermatologist.
No. Keep it clean and use anti infective such as tea tree oil topically to decrease chances of new nail becoming infected.
No. It happens. A new one should grow back. Make sure you are wearing the correct size shoes.