just to add, I'm not sure if 110 would give such symptoms, that seems just a bit low. My
wife has 110 as an average but she suffers no headaches or dizziness. However, those
electronic things are usually out by about 10 either way so I would ask a GP to check your BP with a thingie, the stethascope and cuff method. It has a strange name but I can never remember it.
low bp can obviously cause low pressure because it reduces the oxygen reaching the brain. Sounds to me like you need to chat with your GP. If I take nitrates to open my
vessels during severe angina, I get stonking headaches for about 3 hours so I know what
it's like. There are certain hormones which control the dilation of arteries but that chemistry is beyond me and I'm sure a GP will be able to give good advice.