A Healing Crisis with Reiki would be that of a “cleansing” if you will. So you could experience anything from a cold, flu or GI upset (the releasing) to a runny nose, sore body, fatigue, etc. But most of the time, people don’t experience a Healing Crisis.
It sounds like you might not be well grounded. Try some grounding techniques to ground you back down. Reiki can make you flighty, so visualizing your feet with roots going into the ground and feeling heavy in your feet, etc. can help.