Didnt read that yet, this is all from memory.

From my recollection, the unruh effect is a side effect of referance frames and event horizons. For any given object, you can calculate that objects future path through space time. There will be objects that are too far away for that object to interact with until a certain amount of time has passed. That means those objects are beyond the causality of your original object. This creates an expansign event horizon where anything before it can theoretically be interacted with, and anything past it cannot until the future. The issue is that on the border, on the event horizon, you have virtual particles popping in and out of existance. These particles normally annhilate each other and therefore measurably dont matter. But you have the ability to interact with one without interacting with the other, because its beyond your sphere of influence. But if you can interact with it, it can interact with you. This means you measure a noticable increase in energy at the event horizon because youre only measuring half of the virtual particle, the half that you can interact with and the half that can interact with you.