They look as if they are short of water, or alternatively, the compost is soaked and the corm is sitting in water. Are the leaves soft to the touch?

Maybe too much heat, too. Florist's cyclamen like it cool, around 7º to 18º C.

could be due to thrip damage too, look at the underside of the leaf that also looks a bit pale on the edges. thrips are tiny 1-2mm long thin bodied insects. if you find them then use a spray that is designed for ornamental plants. But they also curl if they have been warm and are now cold. the ones in my conservatory did this after the first frosts. the conservatory doesn't get that warm despite the radiator in there.

as Bulba says could also be a watering issue.

They appear to be planted direct into the ceramic pot - if so it could easily be too wet as there will be no drainage. If it is in a plastic pot with drainage holes but sitting inside the ceramic one check that it isn't standing in a pool of water inside the pot. Cyclamen like a moist atmosphere but not soggy soil. A good idea is to stand the pot on a dish of gravel or small pebbles and keep that moist. The leaves can enjoy the humidity without the soil getting soggy.

Thank you to Bulbaholic, Tugbrethil, Seaburngirl and Steragram for your helpful suggestions. I can't see any sign of thrips under the leaves. It is planted in a plastic pot and I take this out of the ceramic cover and stand it in a two inch deep saucer of water so that it can take up sufficient liquid;
and I use a water meter prob to check on the moisture level. I keep it on a bright window ledge but remove it further into the dining room when the sun is strong. No, the leaves are not soft. However, in spite of this I must be doing something wrong, but what?

It still looks like it is too warm. What is your thermostat set for?

Try standing the plastic pot on a shallow dish of pebbles almost covered with water. The evaporation of the water will give the humid atmosphere that these plants like. If you need to have it in a decorative pot choose one thats considerably bigger than the plastic one and put the pebbles in the bottom of that, but make sure the pot isn't standing in the water. And do heed Tug's advice re temperature. I had one at work once in room where we were always cold - but the cyclamen was very happy...