Hi cjc55.
Welcome to the forum.
Neither Metformin or Vildagliptin have the side effect of making you drowsy. Are you taking any other medication, perhaps not related to your Diabetes ?
The other thing is you mention your Bg level is OK ? Is this throughout the day or just at one particular point in time. High Bg levels can also cause drowsiness.
If you are concerned about this you should discuss with your GP.
Ken.