I have a 14yr old labrador who is acting very strange. She has panic attacks when she tries to come down the stairs and needs to be coaxed down. She is up all night and seems to need to go out every hour but sometimes when she goes out to the garden she just looks confused and runs back in. She has had tests as she was breathless a lot but everything is clear

With the stairs and the backyard she could just be getting a little confused.
Just like with older people, older dogs can forget where they are or what they were supposed to be doing. She could have gotten to the top of the stairs, and forgot all those times she had been up and down them before and suddenly wondered why she is up so high.

Another option is maybe arthritis with the stairs, has she been checked out for that? It might hurt her coming down them.

The vet says she has the start of arthritis in her back legs but did not think this was bothering her at the moment. Perhaps it is.

You should try to get more information from your vet? Has her eating, drinking, or bathroom habits changed at all, you already stated her sleep has? It could possibly be related to arthritis, but I think you should try to consult your vet more. Try to make your dog comfortable. Is there anything in the garden your dog could have eaten?