I can see how you would think your recent reaction to the burnt trees could make you start wondering if this was a sign that treatment had not worked and the recovery you thought you had was in fact not as good as hoped.
Well I can think of something very similar from my own experience. After a very long time, earlier this year, I started reacting due to an incident from long ago - not even a really serious one.I've thread about it however unless you are really keen I'd not go there. I've a good idea what triggered this, not relevant here.
I can to a couple of conclusions. The first is that the symptoms die down to manageable levels very quickly and by now 9 months later are merely the occasional nightmare about this particular incident - they do have to timeshare with other incidents though :-/ Frequency and intensity much less plus. emotions muted as well compared to full-blown attacks in the past
The second is we respond to being in a different state, and they change over time. My psychiatrist says it's due to my increased feelings of security and well-being, my system could afford to let these things out.
The upshot of all this is that if you are anything like me your new reactions may be transitory and more manageable.
I'm sorry your son is not good at the moment