It's not unusual to feel exhausted when struggling with PTSD. It's a challenge for an individual to gain on their ability to slowly gain on reducing how quickly they can go into hyper-aware/hypervigilance where they begin producing a lot of cortisol in the ready for flight/fight. This is also one of the reasons that getting a good night's sleep can be such a challenge. When a person sleeps their brain processes and also cleans out toxins, the body also gains restoratively when someone sleeps. When trauma is involved it can cause night terrors as the brain is trying to figure out how to file it away. That can trigger someone into feeling the event/trauma all over again which can wake them up and trigger them to feel afraid, disoriented, and experiencing an anxiety attack which makes it very hard to go back to sleep.

What people who don't know what it's like to experience PTSD don't realize is that when a person experiences a trigger they get VERY tired as if they just ran a marathon. This is another reason you can feel warn out and dizzy.