timed games

Sorry I’m sure this question is both boring and obvious - I was just playing a 10 minute timed game, down to 3 minutes, I took rook with queen and was up. Opponent took a short while to play and then my turn - within 20 seconds the game “timed out” with a few minutes still left .... and I lost!!! ??? Am I missing something? Was this a glitch? Or does the timer literally go down to 20 seconds as the game nears its end? Haha yes I did have a quick look to try and find the rules and specifically the reason why I lost when I was winning .... but couldn’t!
Any help appreciated. (My partner is currently laughing her head off that I’m commenting about this on a forum) I’m not a sore loser just wanna know the rules! New to this.
Cheers all. 👍

Looks like move 17 used most of your remaining time. Maybe you disconnected and lost extra time... or maybe you lost track of time during the game.

When you look at a game you can see how much time chess.com says you took for each move:

https://www.chess.com/game/live/12975313531?username=drdmorison

Oh, and just to be clear, there are two clocks... one for you and one for your opponent. A clock only ticks down when it's that player's turn to move. So it's possible for you to have 20 seconds left, and for your opponent to have multiple minutes left.

If a clock reaches zero, then the game immediately ends as a loss for that player.

Thank you

Ilama47 - mate that is so helpful thanks I appreciate it 👍👍👍👍

Makes absolute sense now thank you again for taking the time to answer

What does 15I0 as opposed to 15l10 mean?

A|B means each player starts the game with A minutes and every time a player moves, they gain B seconds.

So in a 15|10 game you start with 15 minutes, and pretending you make your first move instantly, after that you'd have 15 minutes and 10 seconds on your clock.