Lying down can help since it makes it easier for the heart to push blood to the brain and the main organs.
Make sure that you drink extra water before going to sleep. Low blood pressure is often a sign of dehydration. We should drink a minimum of 2 litres of water per day to replace everything the body needs to function and eliminate toxins. Often, to simply drink more water can make a huge difference for those with low blood pressure.
Hawthorn or Heart Care from A.Vogel is an excellent heart tonic. See the following text for further information on Low blood pressure or hypotension.