Growth isn't linear. You will have ups and downs in phases or even in moments. Don't be discouraged by human variability.
When you're feeling mechanically down or showing signs of exhaustion, adjust your focus, esp. on your aim training. In particular, you really shouldn't be spending more than an hour on raw non-val "training". It's like spending 4 hours at a gym on a treadmill to prep for soccer. Isn't gonna vastly improve you as a soocer player, actually playing with a soccer ball will. Still, endurance training will help with stamina but you shouldn't overdue it and risk injuries, etc.
Similarly, to get better at Val, you'll eventually need more than just aim/endurance (how many decent aimers are in gold for example) training; you need practice with a soccer ball. So while you're in a phase of apparent decline, just focus on other gameplay elements like util, game sense, IGLing or midrounding. Side note: if you don't wanna do ranked itself to improve and risk losing RR for you and others, swiftplay might be better than tdm for these elements since it mirrors a set of real-feeling rounds. You'll increase your chances of winning, and I promise, your godly aim will come back sooner than you think.
Lastly, with confidence in general, you need more than just one pillar of greatness to have it be up consistently. If your aim sucks on any given day, you should be able to rely on something else to be good/useful to your team (like if you're an initiator main, just following your duelist and dump util for them and then focus on trading).
All in all, remember, human growth isn't linear.
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