Afraid I'll lose too much, or will start gaining, anyone else experience this?

Hi Loosit. I lurk a lot because of reasons, and you guys here have helped me understand the logic, importance and simplicity of CICO. This has led me to, as of today, a 56 lb weight loss. Lately, though, weird things have been going through my mind.

Last week I got some frozen yogurt - the plain, tart kind with a little sugar-free on top. I somehow miscalculated the number of calories per ounce, and believed I had eaten 1500 calories worth of frozen yumminess. Immediately I told myself it would ok, just eat lightly for the rest of the day (this was at noon), and get back on track. I later took another look at the calorie/ounce ratio and realized that yes, when the maths are in my head, the numbers somehow end up in the wrong places. I had eaten about 300 calories of frozen heaven, not 1500. Nonetheless, I was convinced that I've at the very least stopped losing, and thought I possibly was even gaining.

So I hop up on mister scale this morning and I've lost another three pounds. Now I'm wondering if I'll be able to maintain once I reach my goal, or will I continue losing until I'm at a size where being slid under a door becomes an option. I've been at my goal weight the majority of my adult life. I became overweight after the death of someone close to me, and have never at any other time in my life been that weight.

What is up with my worrying about these two extremes? Has anyone else experienced this, or am I just a weirdo? Well, ok, this isn't the only weirdo thing about me, but it's the only weirdo thing about me that bothers me.