ijaz your question is very reasonable and interesting. 5.5 and 8.5 ist mmol? . tats 99 mg and 153 mg ist .
how did you check this ist with glucometer or venous blood
. if with glucometer better don't rely on it . if its venous blood only possible reason is when you exercise the muscles need glucose
so sugar increases and that wil be utilized by the muscles for the energy they need. even then its unlikely that this much of increase is unlikely. if your fasting sugar is this much its good. better you check your post breakfast and post lunch with ur usual medicine and if they are under control don't worry abt this . don't do a strenuous exercise. 30 minutes walk 5 days in a week is sufficient. and check your HbA1c
good luck keep in touch.