Your heart rate will quicken, your nipples may become hard, and blood will start to flow to your genitals.
Rather than just lying on your back, you can try sitting, standing, propping your hips up with a pillow, kneeling on all fours, or any other position in which you find pleasure.
It should feel just like a bump.
What does it feel like? You may find that you enjoy more pressure, or less pressure.