Assalamualaykum, Ahsan Allahu ilayk. i need advice regarding seeking `ilm. in periods i am very attentive, i understand easily, and i study up to 6-8 hours every day. after that has lasted for a while my head feel heavy, i cannot focus. also when this happens, doing ibadah i usually do is hard.

‎What you describe is natural, for the Prophet ﷺ‎ said every deed has a time of zeal and every zeal has a lull, and whoever’s lull is upon the Sunnah is guided (graded ṣaḥīḥ by al-Albānī raḥimahullāh). Take it as a rule: consistency beats intensity, so fix a daily amount you can keep and take a real break every day, as the Prophet ﷺ‎ told Ḥanẓalah, a time for this and a time for that (Muslim).