I have a 5-year-old black labrador and he always curls up like a cat. It's cute, but it also worries me that he may be cold. I read that this may mean they don't feel safe in their environment. Can this be true?
It is completely normal! That is how most of my dogs (now and growing up) have slept!
Most likely normal. Many dogs do this. If it were for another reason such as not feeling safe or not being warm enough, to the point where you needed to do something t help them, there would be other noticeable indications. Curling up, alone, isn't enough evidence that there's anything wrong.
That's a position he may take on for a number of reasons, including temperature or environment, but it's also just a position that a lot of dogs like. Like pretty much any behavior, you have to look at the context in order to determine what it means (or doesn't mean) in that particular instance.
I've sat several large labs and they do sleep or lay in this position occasionally. Both my dogs do too & they are Jack Russell & Jack/beagle mix dogs. I have noticed it's kind of a monkey see monkey do thing! I have very large pillows for the big dogs & they will try & get into the smallest pillows I have lol like they are trying to fit in with the little guys! They displayed this behavior in August when it was warm in our house so I'm sure they were not cold! They were very comfortable with us because my husband had to pick them up & put them into the car, they did not want to go home? kinda embarrassing !
My little dog usually hogs the bigger bed, leaving my bigger dog to curl up into a ball in the small bed. She kinda prefers the tiny bed anyway...