My dr says i can take atenalol as needed being that my bp is normally low to average but same days it spikes for hours. is this true what she says?

Possibly: Atenolol is a weak antihypertensive and not a first line choice. There are potentially better medications if medical therapy is needed. As needed medications are not an ideal option as this could potentially cause large swings in blood pressure. You might want to see a hypertension specialist for further evaluation.

Possible: Depends on how high your blood pressure goes, how frequently this happens and for how long it stays high if untreated. If it stays high only for a couple of hours, by the time you take your medication and it is absorbed, your BP might have come down on its own. If it happens very infrequently it might not be worth taking meds. Might want to try a low salt diet to see if your BP regulates.