A sense of buoyancy is a very personal thing. It is not fixed. It changes over time depending on your physical and mental state. This change can be from second to second or over a whole lifetime.
Having a sense of buoyancy is not about learning how to lie horizontally at the surface of the water, it comes from realising that how your body floats in the water can and will change due to many things e.g
The position of your limbs (including fingers and toes)
The position of your head.
How tense/relaxed you are.
How much breath you have in your lungs.
What you are wearing.
Your perception of your swimming ability.
Your actual swimming ability
How cold/warm you are.
Whether you are in salt water/river water/swimming pool water.
Whether the water is moving (flowing,wavy,choppy)
If you are able to notice how all these (and other) factors affect how you float and more importantly, you allow yourself to accept this in a positive way, your sense of buoyancy will improve greatly and you will feel much more comfortable in the water.