Why all of a sudden my galaxy tab S2 is dead when I wake up?

So I just started having this issue with my galaxy tab s2, (a great tab up2this point) so my bat life will be 75% & after sleeping (7hrs) it is completley dead.? I havnt changed any network settings recently, in fact when in stand by (sleep mode) wifi is off & when i wake my device up it will switch from data to WiFi. Pleas can someone explain to me (that I can) how to fix this.

Welcome to the forums. There may have been an app stuck running. Try charging it and seeing if anything is different. How long have you had the device? It may be possible the battery is aging and can't hold a charge anymore.