Feeling terrible after taking iron pill!

Doc said my iron was low.. She told me to buy Slow Fe iron pills and to take two a day with orange juice. This morning i took one after breakfast, and 10 min later i started feeling super weak and lightheaded with some nausea! Nothing could make me feel better I seriously feelt like i was going to pass out. I took a nap and woke up a little better. Is this normal? I will call my doc first thing tomorrow, its just that im scared to take  my second pill tonight.. 😖