What I was feeling concerned about today was the potential risk of another terrorist attack, as revenge for the US bombing today of caves in Afghanistan that are believed to have been used by ISIS fighters. What does everyone else think
I think ISIS will use any excuse to attack. Even if the US didnt target their cave systems they'd have attacked some one somewhere at some point again in the future.
On a sidenote, I think it's important whether you thing Donald Trump is a strategist or a raging unpredictable idiot. He doesn't make these decisions by himself and the US military forces would have planned/suggested this as a strategy. I saw people losing their shit over it on twitter last night, professing about 'random killings'. It wasn't a random killing. It was a targeted airstrike on a complex network of underground ISIS tunnels. I can't get too upset about it.
Re the nuclear weapons. It's not going to happen. We have our own. As mentioned above. Its not a calculated risk. Those with them know if they use them on us we'll use ours back. Ours are positioned out at sea I believe. Which means anything aimed at us will be destroyed in the air with before it even reaches us. Those countries with nuclear weapons aren't going to be that stupid to put it bluntly.
WW3 is very unlikely because we all are aware of the cost after the first two WWs. Nuclear attack won't happen. As mentioned above, they'll be signing their own death warrant.
A terrorist attack is still more likely, not because of any strikes on ISIS tunnels or because someone's drawn a cartoon of Mohammed, but because this is ISIS and they'd take offence at a woman farting in the wrong direction and plant a bomb somewhere. They're a terrorist organisation. It's what they do, it's their version of chess. Even then, I still wouldn't worry, our secret services do an amazing job of keeping us safe on a daily basis, we only ever hear about the attacks they don't manage to foil, never the several ones that they do manage to intercept. Basically, leave the secret services to worry for you! That's what they get paid for! 
Be vigilant about your surroundings yes but try not to be fearful. It's highly unlikely. I know that's easier said than done, I suffer from anxiety too. We'll be alright. 