Belinda - Its so draining when they are like this. My DD (who is only a few days older than yours) did almost the same thing, went from sleeping at least a cycle thru the day in her cot to flat out refusing and yep I did the same as you, just let her sleep in my arms. Well the last two days she has been happy to have that cycle in her cot again. My thought on this is that they have just gone through a mental development and had their world turned upside down so by us giving them as much security as we can then once they have adjusted they are more happy to be separated from us again.
Google livingcontrolsystems and you can read some excerts from the Wonder Weeks book.
Wonder Week 26:
The World of Relationships
7


At about 26 weeks, your baby will start to show the signs of yet another significant leap in his development. If you watch closely, you will see him doing or attempting to do many new things. Whether or not he is crawling at this stage, he will have become significantly more mobile as he learns to coordinate the action of his arms and legs and the rest of his body. Building on his knowledge of events, he his now able to begin to understand the many kinds of relationships among the things that make up his world.

One of the most significant relationships that your baby can now perceive is the distance between one thing and another. We take this for granted as adults, but for a baby it is an alarming discovery, a very radical change in his world. The world is suddenly a very big place in which he is but a tiny, if very vocal, speck. Something he wants can be on a high shelf or outside the range of his crib, and he has no way of getting to it. His mother can walk away, even if only into the next room, and she might as well have gone to China if he can't get to her because he's stuck
HTH