Are they the lemon tablets that you can dissolve or swallow, or the capsules?
If it's the capsules, they'll be fine. If it's lemon tablets, then they may contain some citric acid which might interfere with ketosis.
But if I'm being honest, I would take them anyway if you're really feeling that rough. You need a good night's sleep more than anything.
You don't need to be in ketosis for this diet to work, remember. If you slip out of ketosis you might feel a little bit hungry, that's all - but as you're going to bed soon, that'll stop you from munching!
Hope you feel better soon x x