My thyroid went downhill really fast after i had DS (was hypothyroid for several years before but only borderline, really).
I didn;t realise for ages what was happening, kept blaming sleepless nights etc when he was tiny, and he didn;t sleep through for a year anyway, but looking back it was obvious
The tiredness means you can;t wake up in the morning, you feel like you are dragging yourslef around. Then when you sit down anywhere anytime you feel like you are going to fall asleep and it's a massive fight not to just curl up and drift off.
By 8pm you feel ready to go to bed.
The thought of doing anything vaguely active terrifies you - exercise, going out in the evening, etc, because you know you will feel even worse afterwards
Everything is a massive effort. Going up stairs, standing for any length of time, pushing a pushchair, etc
You feel depressed because your life feels crap, you have no energy.