What Could Be Causing A Nightly Sensation Of Fluid Moving In My Head, Morning Imbalance, And Unsteadiness While Having Low BP?

I have the feeling of liquid swooshing around in my head when I lay down at night to go to sleep. The liquid is moving for a few minutes and then it settles down. This has been happening each night for about two weeks. I have also had a couple of circumstances where in the morning, I have no balance whatsoever. If I am upright for a few hours, the imbalance passes. I have seen an ENT and there is no fluid in my ears. I have seen my PCP and he wants me to measure my fluid intake and output each day. My BP is quite low 98/57, so PCP reduced my Lisinopril to 2.5 mg / day. I am on Eliquis and Metoprolol. I also have balance issues as I feel unstable on my feet, but not DIZZY. At my PCP visit, there was no mention of further testing and PCP indicated this may be temporary!! I am 83. I have a defibrillator for AF, but otherwise in good health.