Testing fasting blood glucose

When is the best time to test a fasting blood sugar? When I test immediately upon getting out of bed, I usually test between 120-150. However, if I shower and do some things (all still before eating or drinking) and then test, I am usually in the low 100s. I just wonder which is the way I am supposed to test. Thanks for any advice.

Wow, I had no idea a hot shower would lower your BG. I’ll have to remember that! Thanks!