What's happened to my boy???

Took Chase for his usual two o'clock walk today but I don't know what's gotten in to him?

Since wearing the collar he's been acting funny towards other dogs.
We took his collar off him this morning and Matt took him for his first off lead walk since being neutered.
Chase went totally crazy off the lead, I can't say I blame him though, was charging around like a little pocket rocket!

When Matt left and went out the gate Chase saw a neighbours dog that he's usually friendly with but this time he growled and barked at him which I thought was odd.

I then take him out today at two, put on his harness as usual, get ten steps from the gate and Chase was going wild.
Wide eyed, growling aggressively, jumping at the lead and tugging hard on it.
I managed to calm him and kept walking only to then get halfway across a road for him to stop in the middle of it and start tugging on the lead again and snapping at my wrists. This was definitely not play, he was so aggressive towards me!
The only way I could get control was to push him down onto the floor, grab his harness and I don't know how but I managed to re-clip his lead onto his collar and walk back home.
I honestly can't think why or what has happened for him to be this aggressive?!
He was fine this morning with Matt!

Oh and don't know if it's something to do with it but I cane in from getting the kids from school and he turned his back and lasted down in his crate. Usually he's all wags and smiles!

My first thought is that this is just him being unsettled again. I'd fall back on the usual 'relax and go into training mode'. Just for now, don't wait for him to have to think about what he's going to do, ask him to watch you, maybe ask him to follow you away from the other dog, praise him and reward.

Also, keep energy levels low, don't let him get into giddy mode when you're out of the house. That can affect the way they react to various things too.

And, to quote the Hitchhikers' Guide... Don't Panic!

First, im glad you have got him in your name (from your other chipping post) and im glad he has been neutered.

Secondly, this will have been scary fro him..being away from home then suddenly being in pain and having people fawn over him and having a bog random lamp on his noggin.

Third, as said, go right back to basics and start your training again...this never really stops. Keep your calm attitude and slow pace so he relearns that he has to be calm when you want him to.

Hes probably just feeling unsure of things right now and needs stability and normality again.