Suddenly turned nervous

Charlie is almost 4 now, and for the last couple of months has steadily became more and more nervous about things that didn't bother him before.
He is now shying away from passing buses, car doors being opened, carrier bags and rubbish blowing around. Today he was startled by the noise of the poo bag hitting the bin! None of these things were a problem before.
He is great indoors, basic commands no problems and is a great family pet, great natured and a lovely dog so the change in him is quite noticeable.
Outside he becomes deaf to me in his quest to get to other dogs when on his lead and his recall has went to pieces, I've just bought a tracking line again to work on that though. He is now lunging at other dogs and sometimes has a bark and either lunges or shies away from the person he's barked at I'd hate for anyone to think he's vicious when he's anything but.
As he's quite strong the lunging is a problem. I'm finding it very difficult to hold his attention when he spots something he's interested in.
I can't think of anything that would have triggered such nervous reactions in him.
Any advice please.

Have you had a vet check?
Eye or hearing problems might cause him to start more??

Has anything happend that you can think of?
Wilbar has given me great thoughts about stress levels and stuff and i think sometimes if something makes them a little more jumpy then their stress levels hit the roof and make them more likely to react to other things
can you give him a few days of quiet to calm the stress? It deff helps Mia lots to give her some time out from anything she might find stressful

Sounds like something has given him a bit of a fright it might even be a sound when you were out or something? then if he is excited it can change...?

I'd have him checked over to be on the safe side then reward heavily all the times he is 'being brave' i.e. calm in the garden, just outside the garden, walking along the street and so on and try to limit and ignore (to an extent) the worrying behaviours. Start rewarding him when the dog in the street is a spec in the distance and then try to reward closer next time and so on until he is able to eventually walk past...

Just what I would do/try though.

I agree a vet check might be a good idea. Also - think if any changes in his life have occured.
I hope he gets over this soon.

He's recently had a check at the vets, everything was great.
I can't think of anything that's triggered him off really.
Claire and Daisy -I have used a Halti headcollar before on him, certainly helped with the lunging, but I hated it on him and the looks we got, Charlie didn't mind it though so I'll go back to it for a while. Watch me is fine in the house, maybe I didn't reinforce it enough before using it outside, I'll have to work on my timing!
I am taking him out on shorter but more frequent walks, rewarding the good behaviour, and trying hard to see things I think will trigger him off and moving away from them.
He's not a nervous wreck by any means, and yesterday he played quite happily with 3 boxers then came when called which I was quite pleased about,
Thanks for the advice

You could look at Dogmatic headcollars, they come in a variety of colours which definately has an impact on people's opinions. People tend to stop and ask me "what's that on your dog's head?" (great chance to explain that the dog is just scared/reactive rather than aggressive) instead of assuming it's a muzzle. Much more comfortable for the dog IMO too

Thanks- I'll have a look at them, he's definitely not aggressive, I think scared/reactive sums up his recent behaviour. He's a great dog, so I'm hoping this is just a phase and can help him over it soon.