You’re going to want to make every ride a recovery-ride… 50% tops, and probably not more than an hour. You’re essentially going keto for a week or 2. Most keto initiates experience a drastic reduction in power and tte initially, before bouncing back after several weeks.
Electrolyte loading can help as keto (and fasting) is naturally diuretic (you lose a lot of water, and thus electrolytes). In your case, you’re not even eating, thus missing out on even baseline electrolytes from food exacerbating the situation. So you’ll definitely need to augment copious amounts of sodium.