Too much too fast, or a hyper responder. My initial thought fwiw.. you accidentally pinned more than 2.25mg.
Triple check COA matches the advertised mgs, and that you reconstituted correctly.
I started reconstituting 1ml for every 10mg, instead of 1ml for 20mg with Reta, so less concentrated.
The dosages are more forgiving if you're a bit off,or even if the COA is off by a few mgs cause your working with more total volume if that makes sense. And it's a more accurate dose.
I ramped up too fast in the beginning, and had the same experience. The lethargy was so bad I couldn't get a good workout in, even working my day job I had to keep taking breaks to sit. I changed the reconstitution method to the above mentioned as well as pinning 3x/wk and it's been so much better. Actually have noticed the energy people talk about now.
Obviously everything else people are mentioning to, hydration electrolytes eating enough.
Keep us updated bro, hope it subsides soon.