Had v severe, brief diarrhoea 9 days ago. Felt fine. Stools now solid for 8 days but left with nausea, churning stomach, bad fatigue& malaise. Not improving?

Many possibilities.. Most likely this was caused by a microbe; based on your symptoms it's likely a parasite such as Giardia or Blatocystis hominis but some bacteria can cause this too. You could see a Dr. for stool testing but the lab often may not find them even if there. Papaya seeds work as well or better than drugs for most parasite- chew 2 tbsp once every 3-7 days for 3 doses. If not better after that see a Dr.