Nobody panic! (quoting J. Saunders as Edina), 😎
Listen to these three! They know what they are talking about! Their advice is spot-on. If it makes you feel better, I was just in the same boat as you are--my visa was decided in record time (13 business days, non priority). It was an approval. My approval letter was also dated more than a week before the email notification, so that puts UKVI's actual decision five days after receipt of materials. They waited a week before sending me the decided email, which was sent the same day they sent the package back.
I know how stressful it is, though. I actually felt ill when I saw the decision made email (thinking it had to be a quick denial for something). I phoned my husband and he said, "What?! Already?!" We weren't expecting to hear anything until end of November at the earliest.