Can an infected sebaceous cyst drain on its own ? i have one on my chest but when i touch the skin now, i cannot feel any bump underneath anymore.

Self healing: These occur when glands in our skin get blocked and what they secrete collects and causes pressure. Immediate response is inflammation (red, hot, tender swelling). The the body increases blood flow to the injury to bring healing factors to the area and also the veins expand to carry bad stuff away. Avoid picking/squeezing lets nature take its course. Yours probably simply resolved not drained.

Resolve don't drain: Sebaceous cysts do not disappear on their own but infected cysts may resolve giving you the impression that the cyst diaappeared what it has only gotten smaller. If it were to truly drain it would obviously open with pus and a typically foul smelling drainage.

It may come back: Sebaceous cysts usually grow and may get infected. Sometimes they drain out their contents and "go away". But unless the cyst is surgically removed, the cyst contents will likely come back. The best time to remove a cyst is when it is palpable, but not painful or infected.