Frightened of flies?

We think Shula may be frightened of flies. This all started several weeks ago when she suddenly shot out of her basket in the middle of the night. As she wouldn't get back in the basket I removed the cushion to check it and a big black buzzing thing flew out. I hadn't put the light on so couldn't see exactly what it was. By the time I did put the light on, and got the fly spray, the thing had gone, probably through the bathroom window. Anyway she settled down and we forgot all about it, well until two weeks ago. Shula was all relaxed laying on the floor one minute, then suddenly had a panic attack. I thought at first she might be having a fit but she wasn't. She was just trembling and her heart was racing. She didn't want to stay in the lounge, but was fine in the garden. We notice then that there was a fly in the room, I sprayed it and got rid of it and she came back in and was fine. Yesterday she went to lay in her basket in the bedroom and wouldn't come into the lounge, we looked around and finely found a half dead fly on the window ledge. Once we removed it she was okay. I don't think she could have seen it so can only imagine she could hear it. Whether she has been stung and that has frightened her we don't really know. It just seems that when our confident happy dog gets upset by something the timid frightened little dog we first met emerges.