Someone in my backyard 2:40 AM

Sorry for posting another one im new so i just want to tell everything at once, Ok so this was only like 1 - 2 months ago, i was chilling in bed with the curtains open (my bed is next to the window) when there was an light in the hallway to my backyard (yes the is an other route to go in my backyard its an small path) i immediately look outside my window i see nothing, then an other light go on the one that is againts the door (these light are really dim so i cant see shit) idk what that was so i go downstair when im downstair i turned the light on in my house, i looked out the big window to my backyard (its an massive mindow as big as an wall) and i look trough it i feel like being watched but still looked outside then i looked in the mirror (in my backyard there is an mirror in the back) i just saw some light reflecting from inside, then i clearly see something or someone move becaude the mirror light spotted it, i turned the lights off and ran upstairs immediately, I locked my room and my curtains shut and texted my sister who is also home and maybe awake that someone is in the backyard then i calmed down and deleted the text she was not awake i am still a bit scarred to go downstair at night when your in the kitchen and its night everyone can see you thats why im still so scared