I'm a worrier too. I didn't stop worrying about SIDS and the blankets on our bed till dd was probably over 18 months. We put our mattress on the floor when she was a baby so I wouldn't worry about her rolling off (which I did anyway even though it was just probably 10 inches) and I never felt safe enough to bring the bed frame back in, so we're now sleeping with a mattress plus box spring on the floor. She's 4.5 now. She occasionally sleeps over at the grandparents (which was really hard for me for her to be so far away at first!) on a regular, waist-high bed, and I worry about her falling off so the grandparents usually put pillows along the edge of the bed and on the floor. She's fallen off the bed there before, so I don't think that worry/precaution is too over-the-top... though, like skycheattraffic said, mommy instincts certainly can be sometimes!
But, you know... only you know your child and what his/her limitations are, and **I think** it's okay for you to worry based on that. I think my dd had some stop-breathing episodes when she was little, so I probably worried more about sleep safety than other co-sleeping moms. And she has generally been behind the curve when it comes to physical/movement develop and body awareness, so when other moms turn their kids loose I tend to hover a bit more and worry about stuff like falling off the bed. The differences in kids can be really amazing... I remember when my dd and her cousin were both around 18months or 2yo, my mom was playing with dd at a park and sitting at a picnic table. Her cousin is quite physically advanced/adventurous and my mom is used to being around her. So when my mom was sitting with dd on the bench, my mom didn't think to hold/support my dd. Well, my dd fell from the bench onto concrete and chipped a tooth. Kids are just different and have different needs, so different moms have different worries. That's how I justify my worrying instincts at least!