Thanks for response, but unfortunately none applies in my case. My DMM is very much capable of measuing uA currents. Also, although true that measurement impacts current (we all know Heisenberg’s uncertainty principle 
) but as far I know current measurement introduces a tiny resistance in series and hence if anything, should lead to drop in current.
Anyhow, what I discovered (and then just now confirmed from an old post, ([Resolved] Photon Dead After Low VIN) that current drawn in active as well as deep sleep states is function of voltage at vin. And unfortunately, as voltage drops, current consumption increases (reported in the shared link also).
When I powered photon via vin = 5v, current in deep sleep was 70uA. And when I dropped the voltage at vin to ~3.6, the current in deep sleep increased to ~3mA.
ashish