[Solved]-How to get next point in Highcharts tooltip-Highcharts

this need to be done in a few steps:

• get x-index according to x-value: var index = this.series.xdata.indexof(this.x);
• now get y-value: var nexty = this.series.ydata[index+1];

and all you need to do is to sum values, like this: var sum = this.y + nexty;.