Began losartan (25mg) when bp = 131/82. lowered it to 120/74. year later = 114/65. feeling lightheaded. could it be diastolic at 65?

Hypertension: Not sure why the drug started with 130/80. The 114/65 isn't that low but if it really is lower the dizziness could result. Since the need for that drug isn't clear to me, stopping it as a trial is worth discussing with your doc..

BP may be too low: I would not have given medicine for a BP of 131/82 to begin with - that is at worst high normal. The current BP is low enough that you might well get light-headed when standing up or if you get a bit dehydrated. My suggestion would be to either halve the pill or just stop and see your doctor to have it rechecked.