To some extent, this is normal and necessary for the body to adapt to different situations.
Systolic and diastolic arterial blood pressures are not static but undergo natural variations from one heartbeat to another, and throughout the day (in a circadian rhythm). They also change in response to stress, nutritional factors, drugs, disease, exercise, and momentarily from standing up.
For a meaningful comparison, try to measure your blood pressure under similar conditions. For example, take daily measurements at approximately the same time. Try to measure on the same arm, or as directed by your doctor.
Always rest for 5 minutes before you measure your blood pressure.
Occasional high or low blood pressure values are normally no need to worry and are likely to be related to the influencing factors mentioned above. If your blood pressure fluctuates consistently, please consult your doctor.
Older individuals and those who receive blood pressure medications are more likely to have larger fluctuations in pressure. Please check with your doctor which range of fluctuation is normal for you.