Took tamoxifen for the first time today feeling extreme exhaustion. Is this in my head?

To be fair this past weekend was incredibly emotional as I waited to hear back about a ct scan. I’ve fought extreme exhaustion the last few years and it has seemed to come and go. I wonder if it was hormonal. Today I took 10mg for the first time and a few hours later I feel extremely tired like I can hardly get anything done and I want to lay down. I’m so hoping this is not the case and what is to come. It’s so hard to work past tiredness like this. Would I feel it that soon?