In atrial fibrillation (AF), autonomic nervous system (ANS) differences among individuals may have a substantial influence on the varying effectiveness of anti-AF treatments. This work aimed to assess the relationship between changes in autonomic balance and in atrial fibrillatory rate (AFR) oscillations (F_{mathrm{f}}(t)) induced by head-up (HUT) and head-down (HDT) tilt test. 22 persistent AF (psAF) patients underwent a tilt test protocol and ECGs were recorded and analyzed to extract F_{mathrm{f}}(t) and its respiratory modulation (Delta F_{mathrm{f}}). Electrophysiological simulations of stable reentrant rotors in 2D human atrial psAF tissues were performed. Combinations of different levels of parasympathetic stimulation (PSS) by acetylcholine (ACh) and sympathetic stimulation (SS) by isoproterenol (Iso) were tested. The respiratory-related modulation of ACh was modeled by a cyclic temporal variation of ACh. In the patients, HUT/HDT resulted in an increase/decrease in AFR with respect to baseline (BL). Variations in Delta F_{mathrm{f}} from HDT/HUT to BL/HDT were significantly positively correlated with the variations in mean F_{mathrm{f}}(t)(overline{F}_{mathrm{f}}). In the simulations, higher Iso and/or ACh led to an increase in overline{F}_{mathrm{f}}, while Delta F_{mathrm{f}} was correlated to the range of ACh variation. HUT/HDT increased/decreased AFR, which could be explained by an increase/reduction in SS. The concomitant variation in Delta F_{mathrm{f}} could be linked to changes in PSS.