severe flu-like symptoms with profound malaise after intensive meditation
While aches and pains sound very general and while severe chill symptoms are not familiar to me, often various 'excess wind' (prana) &amp; physical/nervous tension (nervous system) symptoms can occur when too much mental energy or 'suppression' is applied to meditation. Therefore, it is likely 'suppression' meditation could result in aches, pains, immature nimittas and other symptoms.
The renowned 'Buddhist' commentary called the 'Visuddhimagga' refers to the 'uggaha-nimitta' and describes the attainment of jhana (absorption) via &quot;suppression&quot; and mental application (&quot;vitakka&quot;). Many Buddhists follow the Visuddhimagga.
However, the techniques &amp; definitions found in the 'Visuddhimagga' in relation to meditation &amp; jhana often have little support in the documented teachings of the Buddha.
To the contrary, the Buddha taught jhana (absorption) is developed by making &quot;letting go&quot; / &quot;surrender&quot; / &quot;relaxation&quot; (&quot;vossagga&quot;) the meditation object, as follows:

And what is the faculty of concentration? There is the case where a monk, a disciple of the noble ones, making it his object to let go, attains concentration, attains singleness of mind. Quite withdrawn from sensuality, withdrawn from unskillful mental qualities, he enters &amp; remains in the first jhana
Indriya-vibhanga Sutta