I played bg match. Got disconnected and I lost everything. My progress, my decks, everything.
Progress and decks would not disappear from a disconnection. If you were logging back into the correct Battlenet account, the likely culprit is having the wrong region selected. You can choose to play in the European, American and Asian regions, and each region is separate, so you would not see your correct progression if you are on the wrong region. Make sure to double check this when logging in.