if voltage is too high but current too low, then is it dangerous for humans?
Current limited high voltage is indeed not dangerous. Static electricity is a good example. 

According to IEC 62368, up to 2mA DC or 0.7mA peak AC is considered safe regardless of voltage. On the other hand 48VDC is normally considered safe but in hospital environment SELV is max 24V. 48VDC can kill you when you have probes inserted inside your body where the electricity can conduct directly through blood vessels. 

With regard to unrestricted current, up to 60VDC or 42.4VAC peak is considered safe.

The key word here is current limited i.e. the current of a high voltage source is limited by means such as series resistor or an active current limiting device. For a capacitor charged to a given voltage there are voltage/capacitance charts that define safe charge level. At 2kV safe capacitance is quite small. 

And, yes, a big electrolytic charged to 1kV will kill you so better stick to small ceramics.