Low LDL & low HDL

Had a triple bypass two years ago.  My recent test showed:  LDL-not on the scale, too low, HDL-22, Triglycerides 116 and total cholesterol 167.  Last year my HDL was 35.  I am taking 20 mg. simvastatin and now doctor has put me on 10 mg. My liver and kidney functions are normal.  What is the reason for the HDL going lower?  I eat all the correct foods as stated in the booklet I received when I had the bypass surgery.  Thanks for your help.

[ed34]

Did you fast before the test?
If your cholesterol was high before your surgery (I presume it was hence the simvastatin), and you have since been more conscious of what you eat, maybe you have achieved the required targets without the meds and they are bringing you too low. But, IS there a too low?
This is something I've often asked Doctors with no reply. How much cholesterol does the body need before you start to get memory loss etc. I'm not sure if anyone knows.