Your problem seems tobe due to 1. Postural hypotension
due to sudden change of posture that is from lying down to standing up posture which happens in peripherral pooling of blood .For evaluation you have to do a dynamic BP check up in each posture and in exercise . This can treated by special exercises and medications . 2. Second possibility is a subclavian steal syndrome in which one side affected as blood is diverted during change of posture or exercise you develop a syncope
3. Third and rare possibility is a vertebrobasilar insufficiency
in which you ge the sane scenario .
All these can treated with medications so dont worry and consult a neurologist
for the evaluation