Is it in any way reasonable to do an IV drip for a temporary boost in energy and mood until I start with the B12?

You could try IV drips at a local naturopathic or functional medicine clinic if you really want. But I'm not really a fan of IV drips because they flood your body with a large amount of nutrients all at once in a short period of time. But what your body really needs to heal is a steady supply of nutrients over a longer period of time.

I did some IV drips years ago and I noticed a boost in energy and motivation for a few hours after. But then the feeling went away and never came back. They didn’t end up being worth it. They didn’t lead to long-term health improvements. IV drips benefit the clinic more than the patient. That was my personal experience anyway. So overall, I don’t recommend it.