Stress or just shyness?

I've got a mature Dumerils boa (about 5 years old)...she's a very docile snake. She typically likes to burrow under her substrate rather than sit in one of her hides all day. When I reach in the tank to let her know I'm there, maybe thinking about picking her up, I usually lightly pet/stroke her...lately she's been tensing up when I do that and if I do it for more than 10 seconds straight she will run into her hide. I don't recall her being THIS timid but I've only had her a couple months. Does this sound like stress or is this pretty typical snake behavior? She used to be way more open to being touched but seems extra timid lately...

Mine reacts the same way. The only thing I can think of is mine is fully settled in and doesn't want to be bothered, unless a rat is present. He doesn't like it when I go to pick him up, but he settles down as soon as I get him out, which is about normal for most snakes...