What can cause sexual arousal to arise abruptly, rarely in meditation, more often in everyday life, although I haven't watched porn. There was one time so strong that without masturbation I would go crazy
Sexual potency is different for everybody, some people have a high sex drive and for some people it's lower. There doesn't really need to be a cause to look for as to why it's so high for you. It could be related to your Natal Chart in some way.
But if it is something that's actually bothering you and kind of interrupts your day. Performing the Ascending Meditation can help you process that energy in a healthy way for your soul and it'll act to empower you as well. Here you go: