Have you ever had signs immediately after conception?

My husband and I are TTC and after having sex last night, about 15 minutes after, I started feeling dizzy. Lasted all night, even woke up with it and finally went away within few hours of being awake. I feel 'off'. I heard you can have symptoms right away from time of conceiving, wondering if anyone here did? And what signs? How'd you know you were pregnant before testing? Thanks!