Thought? Concerns? Safety?
Asleep or fainting?
Fainting. Then falling asleep sometimes. Mostly fainting
Whom are you summoning, I guess would be my first question.
What does your ritual involve is number two.
This is quite common this can be a result of numerous things, such as elemental imbalance, overpowering energy from the spirit, dramatic dimensional shift in the atmosphere of the ritual space.
Energies of the entity overpowering your astral matrix, certain entities can make you fall asleep immediately by raising their energy to a critical degree.
This happened to Eliphas Levi while summoning Apollonius of Tyana. In his case no dangers but, yes, seems like a risky event.
One of the causes may be a change of consciousness, for example from the head to the heart; if the evocator didn’t experienced it in the past nor is ready, he will drop unconscious.
Any dreams you can remember?