Midlife Crisis?

Maybe he was so disappointed in himself for causing Alduin to get thrown through time, that he wanted to eliminate the part of him that caused it.

But then, as he meditated, he realized that Alduin was out of line, hence the reason he helps the Dovahkiin.

Random theory.

You can

Hang your deathbed above the portal and hook it to your magic. Once you're dead, the magic fails and you (and your deathbed) will go to Sovngarde, assuming a [censored] hasn't trolled you and caught it.