My Dr PrescribeD Atenolol For Me, I Took 1/2 Of

My Dr prescribeD atenolol for me, I took 1/2 of 100mg ,as perscribed,first time yesterday morning at 8 .No problems yesterday but this am 4:30, woke up to urinate and heart pounding, feeling anxious. Took blood pressure at 6:30160/94,pulse 57. It's now 6:56 and feeling,bethere now. Pressure last night,9:pm, 129/76, pulse 57. Is it just me getting used to new med. Will be 77 Oct. Female