Let me put it this way, it certainly isn't abnormal.
Many witches talk about feeling different after spell work. Some feel tired, others invigorated. Some of it also depends on the type of magic being performed. I find I put a lot more emotional effort into spells where I am personally involved, recent spell work for my sister left me noticeably drained but a spot of everyday magic to get my own way doesn't really affect my equilibrium.
I'd say on balance being tired afterwards is quite a common consequence of performing magic - however, that said, there are things you can do to minimise it. Don't work magic when you are already tired and run down (unless its urgent) and look at when you are performing magic. I'll do daily off the cuff spells without much preparation but if I'm doing something more involved I will take the time to make sure I am properly shielded and that I have raised energy to utilise for the spell work. I'd also suggest you update your grimoire with particular attention to which spells have a tiring affect on you and learn which ones require a bit more preparation. Like I say, spells with a personal involvement tend to be draining, I also find hexing more depleting than performing "lovelier" types of magic. Get to know what magic wears you out and get your energies ready before you start. And nothing to worry about if you do feel tired - if you think about it magic is all about concentration and you wouldn't expect to do a two hour exam and not be a bit tired by the end of it, would you?
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