The pace felt awkwardly slow, and the heavy legs sounded more like an uncomfortable rhythm than pain. The run still added useful aerobic time, although Sunday's longer outing and several short nights of sleep may have contributed to some residual fatigue.
The heart-rate rise toward 180 bpm did not match the effort you described. Wrist-sensor error is plausible but unconfirmed; later kilometers showed roughly 142 bpm at similar paces. That pattern argues against treating the spike as clear evidence of sustained high intensity.
Takeaway. Trust breathing and perceived effort over a suspicious wrist-HR spike, and keep improving sleep consistency.
Next step. Progressive Easy + Strides. Find a more natural easy rhythm, gently build into steady aerobic running, and finish with two short, relaxed strides.