  We present a detailed timing and spectral study of an extremely variable
narrow-line Seyfert~1 galaxy NGC 4748 using observations in the year 2017 and
2014 performed with AstroSat and XMM-Newton, respectively. Both observations
show extremely variable soft and hard X-ray emission that are correlated with
each other. In the 2014 data set, the source retains its general behaviour of
"softer when brighter" while the 2017 observation exhibits a "harder when
brighter" nature. Such changing behaviour is rare in AGNs and is usually
observed in the black hole binary systems. The "harder when brighter" is
confirmed with the anti-correlation between the photon index and the 0.3-10 keV
power-law flux. This suggests a possible change in the accretion mode from
standard to the advection-dominated flow. Additionally, both the observations
show soft X-ray excess below 2 keV over the power-law continuum. This excess
was fitted with a single or multiple blackbody component(s). The origin of soft
excess during the 2017 observation is likely due to the cool Comptonization as
the photon index changes with time. On the other hand, the broad iron line and
delayed UV emission during the 2014 observation strongly suggest that X-ray
illumination onto the accretion disk and reflection and reprocessing play a
significant role in this AGN.

High Energy Astrophysical Phenomena