Wakefulness fluctuations during rest are a key confound for dynamic functional connectivity. Yet, tracking such fluctuations is not trivial when lacking concurrent EEG and/or eye-tracking. Recent work suggests that ultra-slow CSF fluctuations accompany descent into sleep. Here we evaluate how such fluctuations help track wakefulness in rest scans acquired on non sleep-deprived subjects using sequences not optimized for detecting such inflow-related fluctuations. We conclude that those fluctuations can be easily detected in other samples, and that they may provide valuable time-resolved information about fluctuations in wakefulness, as well as a means to segregate subjects according to their overall wakefulness levels.