Svarga is, figuratively speaking, where I go because of good karma. But a limited action always brings a limited result, so a stay in heaven also ends, just as a heavenly feeling is temporary. Experience takes place in the mind. So mind management means doing the right dharmic action and cultivating the right dharmic thoughts, so that the mind becomes a heaven, and not a hell.

The Upanisad describes heaven as concealing darkness. Why? My karma has been so focused on longing (sakāma) for a better life or heavenly spheres that my constitution (subtle body) is turned outward, towards material, worldly or heavenly pleasures. This is what is meant in the īśa upaniṣad verse 9 with:

andhaṃ tamaḥ praviśanti ye'vidyām upāsate

tato bhūya iva te tamo ya u vidyāyāṃ ratāḥ

Those who are focused on rituals (this can also mean modern strategies against precariousness) in order to benefit from it, enter blinding darkness (from svarga loka).

Into even deeper darkness go those who focus on god-worship (brahma loka, a kind of super-heaven).

This is just as bold, but having said that, the same īśa upaniṣad, immediately afterwards, states: "But whoever practices both (karma yoga and upāsana yoga), not as an end in itself, but as a means of freedom, will taste infinity in the end."

For example, heaven seems like a lot, but it is better to focus here and now (sadyomukti) in normal earthly life on moksa, freedom from (and therefore also for) the living, individual being (jīvan-mukti).