Can you tell me what it's like to have a "separate sesamoid" ?

Maybe fine?: You did not say if the sesamoid is in your foot or hand. Sesamoid bones are small bones that are embedded in tendons to improve muscle effectiveness. Usually they develop from a single ossification center. Sometimes they may develop from two or more ossification centers. This is generally asymptomatic, but if painful it should be checked out by the appropriate hand or foot specialist