Pening NK Pitam Tiba2

Is it normal tgh baring tiba2 rasa pening & menarik macam nak pitam tiba2. Sbb sblm preggy perkara itu dah biasa bg sy. Tapi masuk 22minggu ni, 1st time jadi. Is it normal? Sebab sebelum tu perut mengeras. Sbb tu baring je. Tapi rasa nk Pitam after few hours