I had felt this feeling before. A great euphoria followed by a low, mixed with churning anxiety and a sense of not being able to cope.
Being an owner of horses for the first time was like having my first baby. The high when they arrived lasted exactly 2 days, although I did have to constantly walk over to the stables to check they were still alive - just like poking a sleeping baby to check they were breathing.
Then day 3, when typically the new mama experiences a bout of the 'baby blues', a hormonal dive after the birth of a newborn. Anxiety can make an appearance and feelings of not being good-enough may emerge.
I got the pony-blues on day 3. Had I done the right thing? Do I know enough about horses? Can I afford to do this? What if she bucks me off? She's too young! I'm too old! This is nothing like I imagined it would be!
I then called some people who calmed me down and encouraged me that I would make a wonderful pony-mama. Just one day at a time, starting with grooming and washing them, taking them for a walk down the lane and a munch on a rare patch of grass. Beginning by touching them and knowing every inch of their bodies to understand what is normal for them, finding their likes and tickly spots, accepting their flaws and not expecting instant results.
Of course the reality is nothing like I imagined - but then, neither was becoming a mother for the first time. This didn't stop it being the best experience of my life.