Is it normal to have high bp that goes away after a hour or two. but comes back after a long time like a month or two. thanks ?

Blood pressure: readings can be highly variable and your definition of "high" may not be accurate. There are diseases that can cause the blood pressure to be intermittently very high and then very low. You should keep a record of your recordings for a few weeks and then make an appointment for evaluation with a health care provider.

BP is a behavior,: constantly changing. Each measurement=from a single heart beat for the top (Systolic) value, another different single heart beat for the bottom (Diastolic) value. A mercury manometer & stethoscope (or sensation in artery under cuff) =most accurate. Aneroid gauge less accurate, digital least accurate (these systems, oscillometric method, guess at the values). The values can & do change quickly.