Owners of cats know that cats love to lie at different places. From your computer table to the dining table they will spare no surface. This is because they try to seek our attention and they are often successful in doing so. Cats can sleep up to 16 to 20 hours per day, and you will see them falling asleep almost anywhere, anytime.
If your cat is sleeping only on the floor it may be normalizing its temperature. It is pretty common among cats to lie on cold surfaces to cool themselves. The cat may feel uncomfortable when the temperature in your house exceeds 24 degrees Centigrade.
This Is How Cat Nature Is

You often see your cats lying around on almost anything they may find. They will sleep on pieces of paper, folded laundry, or with you in your bed. But suddenly your cat may stop sleeping anywhere except on the floor. If you find it weird, actually it is not. This is actually a cat nature and all cats whether they are living out in nature or in our homes, love to sleep on hard surfaces.
It may be Temperature

Cats are good at moderating their body temperature. As soon as summer approaches, you will find your cat sleeping on the cold tiles to cool off its body temperature.
It is not unusual that when the indoor temperature reaches around 23 – 25C, most cats prefer lying on the floor. They find laying on hard surfaces the easiest way to cool them.
In summers, they lie on hard and cold surfaces such as cold tiles or wood floors. However, in winters, you may find your cat cuddled on the carpet.
They May Be Sick

Illness is the second most common reason that a cat suddenly starts sleeping on the floor. They may go in this position to calm their aching body. Cat sleeping positions when they are sick is an important indicator of the type of ailment they are suffering from. This can be very helpful for the vet to diagnose the actual problem.
Most often lying in cold places is related to pain relief. The cold and hard surfaces are more relieving for a sick cat than the soft surfaces like beds, rugs, and towels. A cat will lay in a litter box or on your bathroom floor in an awkward position if her symptoms are worse such as an upset tummy and vomiting.
Is my Cat Really Sick (Symptoms of Most common diseases)
As cats are good at hiding pain, most people will panic when they notice an unusual sleeping position. But there are a few other symptoms that will differentiate a cat in pain from a normal cat.
If they are in intense pain their pupils dilate and they might squint. Illness also decreases the mobility levels of the cat. The cat will become lethargic, will not groom itself, and will not roam around the house as usual. It will also start growling, swatting, or snapping when you will touch her.
It indicates that the cat has developed feline idiopathic cystitis, a UTI specific to cats If the cat is touching near the genitals, having difficulty in passing urine, or having blood in the urine. In this condition, the cat will lie on a hard surface to relax her bladder.
When cats develop Arthritis, they start avoiding human contact because they do not like anyone touching them. The cat will hide and sleep in places that are difficult to reach such as under the bed or in the garage.
Sick cats also start soiling the house instead of using their litter box. This may be due to intense pain and inability to position themselves properly in their litter box.
Old cats prefer sleeping on hard surfaces because of aging they feel it difficult to regulate their body temperature. Sleeping on the floor not only regulates their body temperature but also helps in their aging pains and arthritis.
Is My Cat Expecting

Pregnant cats prefer sleeping on hard and cold surfaces. This is because they are carrying an extra weight which makes them uncomfortable. Especially if it’s late summer they will do an extra bit of effort to keep their bodies cool. This is why she will sleep on the floor throughout her pregnancy.
Conclusion
If your cat has suddenly stopped sleeping in bed, there is nothing to worry about as long as she is comfortable and not acting out of the ordinary. Until and unless your cat is sleeping at a position where you can step on it or trip over it, you can let her sleep there.
Cats change their sleeping spots due to a number of reasons mentioned earlier. But cats sleeping on the floor in strange positions may indicate health issues such as arthritis, idiopathic cystitis, pregnancy, or any other disease. Sometimes stress may trigger them to sleep in strange places for example if you bring a new pet into the house, the cat will try to avoid it.