Welcome to HealthcareMagic,
Looks like your symptoms could be due to low blood pressure or low sugar levels. So your aim should be to maintain your blood pressure and sugar levels. My advice is:
1. Do not skip your meals, have regular meals and if your feeling giddy have something like a chocolate or
glucose drink to correct your blood sugar levels.
2. Have a died rich in salt for a couple of days
3. Drink plenty of water
4. Do regular exercise which will improve your
muscle tone and improve your blood pressure and blood sugar levels.
5. Avoid alcohol
6. Be careful when rising from lying down or sitting. Pump your feet and ankles a few times before standing up. When getting out of bed, sit upright on the edge of the bed for a few minutes before standing.
Even after following my advice ,If you are getting frequent problems then visit your physician for a detailed evaluation.
Hope that answers your question.
Regards, Dr.Imaad.