I think with your deadlifts you need to be very careful of how you lift.
Many people try to push too hard on higher weights and thus losing their form.

Next time you deadlift make sure your not using any of your upper body strength. It is difficult to realize but many people do this to help buffer the weight. This causes your neck muscles and traps to contract while you lift and it might be the cause to your headaches.

when you deadlift do you feel your nape area tensing too much. then you might have to fix that part as it will strain you upper body and you will feel dizziness and headaches.