I lost all of my Raid progress.
Raids are six-player co-op missions that can take several hours to complete. As such, Raids can be paused and resumed at another time provided the Fireteam leader is the same player throughout the Raid. However, Raid progress is counted over the course of a week and is reset every Tuesday morning at 9:00 AM UTC.
If you are participating in a Raid, be sure to complete it before the reset time in order to receive loot and experience from the Raid.
The following link can assist with converting UTC to your local timezone.