I have it and am barely affected by it. It got spotted in a general blood test years ago when trying to diagnose why I was fainting. I just take my 150 micrograms (never realised that was a rarely high level) every morning and carry on with my day. If I forget to take them one morning, meh, no ill-effects.
Very occasionally, i.e. two or three time a year, I begin to realise my levels have gone a wee bit skewy because I am showing all the signs of being hypo- or hyper-. The most noticeable sign is to do with sleep. All I have ever had to do is wait a couple of days and everything’s back to normal.
But really, although I’m not affected by it I can use it as an excuse for everything! Can’t be bothered doing something? Forgot something? Put on a bit of weight? Sleepy? Grumpy? “Yeah, feels like my levels are maybe a bit low.” NEEDING to go out for a ride as you’re getting antsy sitting in the house? I can also blame that on my thyroid! It’s brilliant.
It’s much tougher on others. Both my sisters also have it, one of them has levels that are constantly fluctuating so she is, genuinely, always suffering the symptoms one way or another.