I had terrible dizzy spells throughout the 2nd and 3rd trimester, they drove me insane. When I asked the midwife about it. She said because my blood pressure is fine that it's most likely to be my blood sugar levels. She said whenever it happens to eat something like an apple, so I did and it helped heaps. She also said when you go from laying down to standing do it in stages, so go from laying to sitting and wait a few seconds then sitting to standing and wait a few seconds before you walk lol i hope they don't hang around because they really are horrible