You need to set your own targets. Ones you are comfortable with. Once you reach these targets most of the time, you can lower them.
The best target, in my opinion, is to try to keep any rise from before eating to the 2 hour mark definitely under 2mmol/ and preferably a lot less. Once you can do this regularly at each meal, your base line numbers (fasting and before meals) should come down to near non-diabetic levels. My personal target is between 4 and 7.
Medical treatment is not normally required unless your levels go to the 20's and you feel rotten. Hopefully yours are nowhere near this. As for being too low, for a T2 on diet only or Metformin, under 4 maybe considered too low.