Is it normal to go back to feeling so terrible after feeling something close to normal (whatever that is)?
I won't use the word "normal", but it's very common and typical. It means you need a dose increase. No MD ever warns us that this will happen, but it does.
When your body starts getting some of the hormone that it needs after being so long without having enough, you start to recover a little. Then, after that initial dose has been absorbed and "used up", your body starts screaming for more. If you're lucky, your MD will agree and increase the dose; if he's thyroid-ignorant like so many are, and he doses by TSH alone instead of FT4 and FT3, you may not get the increase.
Sooooo.... I hate to tell folks this, but don't expect to feel all better until you reach your optimum dose and have been on it for a few months.