Praise be to Allaah.
So long as there is no intercourse or emission of semen, whether awake or asleep, following ghusl (complete ablution), it is not necessary to repeat the ghusl, and ones prayer is valid. Any maniy (prostatic fluid) that has gotten onto one's clothes needs to be washed away.
And Allaah knows best.
Sheikh Muhammed Salih Al-Munajjid