never felt an orgasm and almost did w my boyfriend and freaked out. help??

My boyfriend was fingering me and I've never orgasmee before but I felt like I go close and suddenly it felt like I had to pee and I freaked out internally and made him stop because I felt like if I let go I'd pee on him. What does an orgasm feel like? How does it start off? Can I possibly pee during an orgasm? Any tips help