Also and i know this a long shot at best one reason doxycycline helps me perhaps is that it increases allopregnanolone or other neurosteroids. There is no direct evidence for this yet but i note :
From wiki:
Several studies using minocycline and doxycycline, in an animal model of Alzheimer’s Disease, have indicated that minocycline[19][20] and doxycycline[21][22] exerts a protective effect in preventing neuron death and slowing the onset of the disease.
Allopregnanolone has been shown to aid the neurogenesis that reverses cognitive deficits in a mouse model of AD.[14]
Whilst it might not be through allopregnanolone it might be through a different mechanism involving neurosteroids. My sleep on doxycycline is better than without it.