Definitely assess how much your "mental state" and how it changes over time during listening might be a factor. Listening fatigue over time is not uncommon, and could be the cause with what you are noticing just the symptom.
VEry good idea to leave the room and come back. THat allows your ears to "reset" and make a second unbiased assessment of what you are hearing.
Then also make sure everything is set up correctly and in good operating condition, though this is often easier said than done. When a component system does not sound "right", the only way to determine the cause is via a series of regression tests, where you change one thing at a time and notice any differences, until finally you identify a prime culprit or suspect and then take corrective action. I always keep spare components around that I can substitute one by one to help identify where an issue may exist, but many may not have that option.
If everything appears to be in order, then next it is time to try easy no cost tweaks, like tweaking speaker placement, toe-in, listening position. etc.
THen once all else fails, you are in a better position at this point to really assess what kind of upgrades, if any, might help.
It all takes time and patience. ITs easy to try to throw money at the problem, but what is really needed first is knowledge and understanding of why something is either working or not.
IF changes are needed, buying used and not overpaying is a good strategy to enable experimentation without paying an unnecessary premium along the way.
