When you're actually in Alpha and Theta, can you tell, and how do you know?

When you're actually in Alpha and Theta, can you tell, and how do you know

Yes, you can tell and one way is for someone else to observe your rapid eye movement (REM). Sometimes you can feel your own REM. You will know when you're in the Theta state because you actually do not feel your body (it's as though it's numb) yet you have total control and your mind is extremely lucid. The other mechanical way is by measuring your brain waves with the electro-encephalograph (or other devices designed for this purpose).