How can I tell if I’m about to orgasm?

I’ve masturbated before but never really felt anything from it. Last night I tried the shower head and it was amazing (like seriously). My legs were shaking and my breathing was different and I felt like I had to shut my eyes from the amount of pleasure. I stopped because ive read on here about your body going into shock from over stimulation? I’m just kind of worried since I don’t know what it supposed to feel like 🤦🏼‍♀️. Help a girl out?