Is it possible ADHD explains why I'm always exhausted from thinking?

Yes. Many adults with ADHD describe constant mental fatigue, even on days that don’t seem demanding. This happens because tasks that are automatic for others require conscious effort. Planning, remembering, switching tasks, filtering distractions, and regulating emotions all consume cognitive energy. Over time, this creates a feeling of being mentally drained without a clear reason. Rest alone doesn’t always fix it because the fatigue isn’t physical, it’s executive. Once people understand this, it often explains why they feel tired despite not “doing that much.”