A Dual Orexin Receptor Antagonist to Reduce Biomarkers of Neurodegeneration in Adults With Insomnia.

The goal of this clinical trial is to explore the potential neuroprotective benefits of a dual orexin receptor antagonist (DORA) in adults with insomnia. The main questions it aims to answer are: * Does the DORA reduce blood-based phosphorylated TAU181, in adults with insomnia, when compared to placebo * Does the DORA reduce other blood-based biomarkers of neurodegeneration, including phosphorylated TAU217, amyloid beta 40:42 ratio, Neurofilament Light Chain (NFL) and Glial Fibrillary Acidic Protein (GFAP), when compared to placebo. Participants will: * Take 10mg Lemborexant nightly for two weeks * Take a matching placebo nightly for two weeks * Visit the research institute for a screening visit and for an overnight visit at the conclusion of each study drug treatment (3 visits in total).