If you feel confident that you can fix it yourself then put it in the truing stand and loosen the spokes in those flat areas. Be sure to loosen the same number of left and right pulling spokes in each area so that the wheel stays in true. Also turn each spoke the same amount, try 1/4 turns to start with then check the lateral trueness of the wheel, correct if necessary, then check the flat spots and repeat the loosening if necessary. As far as slowing you down, it is probably not noticeable but a rim with flat spots could cause your brake pads to contact your tire sidewalls at those sections when the brake is applied. It also could yield a bumpy ride.