If I turned back around and someone was standing right in front of me, I might do any of the following:
- Gasp, scream or inhale deeply;
- Jump, fling my hands or do some other stupid jesture because I am so startled;
- Wet my pants (depending on how startled I was);
- Run the other way (or atleast feel like running the other way)
Here’s how I might decribe my startled character: Jane turned back around, yelped and threw her hands up to her mouth. She stared wide-eyes at Tom standing right in front of her. “Finally, you’re back,” she said, throwing her arms around him. “I can’t believe you’re here.”
A rought example, but still fun to try and describe.