Ejaculation is the discharge of semen (usually containing sperm) from the male reproductory tract, normally accompanied by orgasm. It is usually the final stage and natural objective of male sexual stimulation, and an essential component of natural conception. In rare cases, ejaculation occurs because of prostatic disease. Ejaculation may also occur spontaneously during sleep (a nocturnal emission or "wet dream"). Anejaculation is the condition of being unable to ejaculate. Dysejaculation is ejaculation that is painful or uncomfortable.