[Westleigh]

I think it could be one or both of a couple of things. You should make sure you are well hydrated before doing energy work of any sort (including meditation and yoga). These activities cleanse your energies, which in turn causes your body to cleanse itself of toxins, which uses a great deal of your body's water reserves. I remember the first time I had reiki done on me I felt very thirsty afterwards and was confused about it until the practitioner explained this to me. Dehydration can cause you to feel tired and lack energy.

It may also be because the spiritual and emotional healing and raising of your energies that is part of this kind of spiritual work causes recovery and strengthening of your physical body along with your spirit body, and just like when your body is recovering from an illness, this physical recovery process can cause you to feel tired and weak for a while - of course, in the long term, you will feel much better than you did before.

It sounds to me like you are engaging in some significant emotional and physical healing with your practice, even if you're not aware of it - that's good, it means you are doing it right! If you find it is draining you too much, just hold off on the meditation for a couple of days or meditate for shorter periods so you can regain your balance. Spiritual growth can be quite intense at times so make sure you don't overdo it. It's like exercise - incredibly good for you but doing too much of it at once can wear you out and cause exhaustion. Keep going on your spiritual journey, but be sensible about it and take care of yourself.