It is tempting to use a better day to catch up on everything. When activity can lead to a delayed crash, that understandable urge may create a difficult cycle. Pacing is an attempt to make demands more manageable, not a guarantee that symptoms will stay under control.
Look beyond the activity itself
Include preparation, travel, concentration, conversation, and recovery when deciding what a task costs. A short appointment may involve far more effort than the minutes spent with the clinician. An activity can feel tolerable at the time and still affect you later.
For ME/CFS, the CDC describes post-exertional malaise and individualized activity management. Generic exercise targets and fixed increases may be inappropriate; a plan needs to account for your condition and response.
Make space for adjustment
Break a task into smaller parts when useful, simplify it, delegate it, or decide it can wait. Keep a brief record of patterns only if that helps rather than adding another demand. A wearable may offer information, but a heart-rate number alone cannot tell you an activity is safe.
Work with a clinician who understands post-exertional symptoms if you can access one. If a crash happens, respond with care rather than blame. Illness is not fully controllable through planning. You deserve support even when you have paced thoughtfully and still feel worse.